Add Prometheus and Grafana to Docker Compose (paritytech#221)

* Add Prometheus and Grafana to Docker Compose

* Expose relay's Prometheus metrics port

* Use Docker network references intead of localhost

When you have containers on the same network they don't communicate
over localhost, they instead refer to their container names

* Move dashboard components into deployment folder

* Update folder structure for Grafana and Prometheus config files

The new folder structure more closely matches the expected defaults
by Grafana and Prometheus, which allows us to clean up the paths
in our docker-compose file a bit.

* Add documentation about Prometheus and Grafana

* Refer to Prometheus server instead of node

bridges/README.md

@@ -161,10 +161,10 @@ The folder structure of the bridge relay is as follows:
 To run the Bridge you need to be able to connect to the RPC interface of nodes on each side of the
 bridge (home & foreign chain).
 
-You can build the relayer using [./Dockerfile](Dockerfile), which will use all the local source
-files,
+You can build the relayer using [./Dockerfile](Dockerfile), which will use all the local source files,
 or you can use an image that is designed to build from Github repo sources (`master` branch by
 default, configurable via `build-arg`):
+
 ```bash
 docker build \
   https://raw.githubusercontent.com/paritytech/parity-bridges-common/master/deployments/rialto/Bridge.Dockerfile \
@@ -173,7 +173,8 @@ docker run -it poa-relay
 ```
 
 By default the relayer is configured to connect to OpenEthereum `--dev` chain node and Substrate
-`bridge-node` running in a `--dev` mode.
+`bridge-node` running in `--dev` mode.
+
 To build the `bridge-node`:
 ```bash
 docker build \
@@ -184,13 +185,12 @@ docker run -it bridge-node
 ```
 
 And to build `OpenEthereum` with bridge support:
-```
+```bash
 docker build \
   https://raw.githubusercontent.com/paritytech/parity-bridges-common/master/deployments/rialto/OpenEthereum.Dockerfile
   -t openethereum
-docker run it openethereum
+docker run -it openethereum
 ```
 
-See [./deployments/README.md](Deployments README) to learn more about how to run
+See [Deployments README](./deployments/README.md) to learn more about how to run
 a more sophisticated test network using `docker-compose` setup.
-