Add plugin status http GET and document the HTTP api

SERVERPLUGINS.md

@@ -17,3 +17,23 @@ In essence a plugin is an npm module with `signalk-node-server-plugin` keyword i
 The module must export a single `function(app)` that must return an object with functions `start(configuration)` and `stop` and a field `schema`. The schema value should be the structure of the plugin's configuration data as [JSON Schema](http://json-schema.org/).
 
 See [MarineTraffic Reporter](https://github.com/tkurki/marinetrafficreporter) for an example.
+
+##HTTP API
+
+###`GET /plugins/`
+
+List of installed plugins with their configuration data.
+
+###`GET /plugins/<pluginid`
+
+```
+{
+	"enabled": false,
+	"id": "marinetrafficreporter",
+	"name": "Marine Traffic Reporter"
+}
+```
+
+###`POST /plugins/<pluginid/configure`
+
+Save configuration data for a plugin. Stops and starts the plugin as a side effect.

lib/interfaces/plugins.js

@@ -32,7 +32,7 @@ module.exports = function(app) {
 
       router = express.Router();
 
-      app.use('/plugins', function(req, res, next) {
+      app.get('/plugins', function(req, res, next) {
         res.json(app.plugins.map((plugin) => {
           var data = null
           try {
@@ -108,6 +108,14 @@ function registerPlugin(app, pluginName) {
 
   var router = express.Router()
   router.use(bodyParser.json())
+  router.get("/", (req, res) => {
+    const options = getPluginOptions(plugin.id)
+    res.json({
+      enabled: options.enabled,
+      id: plugin.id,
+      name: plugin.name
+    })
+  })
   router.post("/config", (req, res) => {
     fs.writeFile(pathForPluginId(plugin.id), JSON.stringify(req.body, null, 2), function(err) {
       if (err) {