feat: add functionality to register plugins via http

Also:

- Add functionality for serving the responses from plugins
- Add tests for related methods and routes

Closes #2, #37

package.json

@@ -25,6 +25,7 @@
     "preversion": "npm run prepublishOnly",
     "push": "git push && git push origin \"v$npm_package_version\"",
     "start": "NODE_CONFIG_ENV=elasticsearch ALLOW_NO_TRANSPORT=true node ./lib/cli.js",
+    "test": "env NODE_CONFIG_ENV=elasticsearch ALLOW_NO_TRANSPORT=true nyc mocha --require ts-node/register --ui mocha-typescript --exit 'test/**/*.ts'",
     "tslint": "tslint -p tsconfig.json -c tslint.json 'src/**/*.ts'"
   },
   "dependencies": {
@@ -35,12 +36,14 @@
     "config": "3.1.0",
     "cors": "2.8.5",
     "elasticsearch": "16.1.1",
-    "express": "4.17.1",
     "express-promise-router": "3.0.3",
+    "express": "4.17.1",
     "fs-extra": "8.0.1",
+    "got": "9.6.0",
     "jsonschema": "1.2.4",
     "moment": "2.24.0",
     "morgan": "1.9.1",
+    "nock": "10.0.6",
     "node-cache": "4.2.0",
     "node-cron": "2.0.3",
     "nodemailer": "6.2.1",
@@ -50,20 +53,34 @@
   },
   "devDependencies": {
     "@openstapps/configuration": "0.21.0",
+    "@types/chai-as-promised": "7.1.0",
+    "@types/chai": "4.1.7",
     "@types/config": "0.0.34",
     "@types/cors": "2.8.5",
     "@types/elasticsearch": "5.0.34",
     "@types/express": "4.17.0",
     "@types/fs-extra": "7.0.0",
+    "@types/got": "9.4.4",
     "@types/morgan": "1.7.35",
+    "@types/nock": "10.0.3",
     "@types/node-cache": "4.1.3",
     "@types/node-cron": "2.0.2",
     "@types/nodemailer": "6.2.0",
     "@types/promise-queue": "2.2.0",
+    "@types/sinon-express-mock": "1.3.7",
+    "@types/supertest": "2.0.7",
     "@types/uuid": "3.4.5",
+    "chai-as-promised": "7.1.1",
+    "chai": "4.2.0",
     "conventional-changelog-cli": "2.0.21",
+    "mocha-typescript": "1.1.17",
+    "mocha": "6.1.4",
+    "nyc": "14.1.1",
     "prepend-file-cli": "1.0.6",
     "rimraf": "2.6.3",
+    "sinon-express-mock": "2.2.0",
+    "sinon": "7.3.2",
+    "supertest": "4.0.2",
     "tslint": "5.18.0",
     "typedoc": "0.14.2",
     "typescript": "3.5.3"