First RESTful HTTP API (#399)

* Added generated code for REST API.
 - Created a new crate rest_api, which will adapt the openapi generated code to Lighthouse
 - Committed automatically generated code from openapi-generator-cli (via docker). Should hopfully not have to modify this at all, and do all changes in the rest_api crate.

* Removed openapi generated code, because it was the rust client, not the rust server.

* Added the correct rust-server code, automatically generated from openapi.

* Added generated code for REST API.
 - Created a new crate rest_api, which will adapt the openapi generated code to Lighthouse
 - Committed automatically generated code from openapi-generator-cli (via docker). Should hopfully not have to modify this at all, and do all changes in the rest_api crate.

* Removed openapi generated code, because it was the rust client, not the rust server.

* Added the correct rust-server code, automatically generated from openapi.

* Included REST API in configuratuion.
 - Started adding the rest_api into the beacon node's dependencies.
 - Set up configuration file for rest_api and integrated into main client config
 - Added CLI flags for REST API.

* Futher work on REST API.
 - Adding the dependencies to rest_api crate
 - Created a skeleton BeaconNodeService, which will handle /node requests.
 - Started the rest_api server definition, with the high level request handling logic.

* Added generated code for REST API.
 - Created a new crate rest_api, which will adapt the openapi generated code to Lighthouse
 - Committed automatically generated code from openapi-generator-cli (via docker). Should hopfully not have to modify this at all, and do all changes in the rest_api crate.

* Removed openapi generated code, because it was the rust client, not the rust server.

* Added the correct rust-server code, automatically generated from openapi.

* Included REST API in configuratuion.
 - Started adding the rest_api into the beacon node's dependencies.
 - Set up configuration file for rest_api and integrated into main client config
 - Added CLI flags for REST API.

* Futher work on REST API.
 - Adding the dependencies to rest_api crate
 - Created a skeleton BeaconNodeService, which will handle /node requests.
 - Started the rest_api server definition, with the high level request handling logic.

* WIP: Restructured REST API to use hyper_router and separate services.

* WIP: Fixing rust for REST API

* WIP: Fixed up many bugs in trying to get router to compile.

* WIP: Got the beacon_node to compile with the REST changes

* Basic API works!
 - Changed CLI flags from rest-api* to api*
 - Fixed port cli flag
 - Tested, works over HTTP

* WIP: Moved things around so that we can get state inside the handlers.

* WIP: Significant API updates.
 - Started writing a macro for getting the handler functions.
 - Added the BeaconChain into the type map, gives stateful access to the beacon state.
 - Created new generic error types (haven't figured out yet), to reduce code duplication.
 - Moved common stuff into lib.rs

* WIP: Factored macros, defined API result and error.
 - did more logging when creating HTTP responses
 - Tried moving stuff into macros, but can't get macros in macros to compile.
 - Pulled out a lot of placeholder code.

* Fixed macros so that things compile.

* Cleaned up code.
 - Removed unused imports
 - Removed comments
 - Addressed all compiler warnings.
 - Ran cargo fmt.

* Removed auto-generated OpenAPI code.

* Addressed Paul's suggestions.
 - Fixed spelling mistake
 - Moved the simple macros into functions, since it doesn't make sense for them to be macros.
 - Removed redundant code & inclusions.

* Removed redundant validate_request function.

* Included graceful shutdown in Hyper server.

* Fixing the dropped exit_signal, which prevented the API from starting.

* Wrapped the exit signal, to get an API shutdown log line.

beacon_node/client/Cargo.toml

@@ -9,6 +9,7 @@ beacon_chain = { path = "../beacon_chain" }
 network = { path = "../network" }
 http_server = { path = "../http_server" }
 rpc = { path = "../rpc" }
+rest_api = { path = "../rest_api" }
 prometheus = "^0.6"
 types = { path = "../../eth2/types" }
 tree_hash = { path = "../../eth2/utils/tree_hash" }