[ACA-1743] extension settings (#1399)

* upgrade tslib

* initial settings skeleton

* migrate language picker setting

* support string parameters

* remove process extensions workaround

* update extensions schema

* update docs

* unit tests

* fix unit test

package.json

@@ -91,8 +91,8 @@
     "codelyzer": "^5.2.2",
     "commander": "^4.0.1",
     "cpr": "^3.0.1",
-    "dotenv": "6.2.0",
     "cspell": "^4.0.55",
+    "dotenv": "6.2.0",
     "husky": "^2.4.0",
     "jasmine-core": "~2.8.0",
     "jasmine-reporters": "^2.2.1",
@@ -116,7 +116,7 @@
     "selenium-webdriver": "4.0.0-alpha.1",
     "ts-node": "^8.0.3",
     "tsickle": "0.34.0",
-    "tslib": "^1.9.0",
+    "tslib": "^1.11.1",
     "tslint": "^5.20.1",
     "typescript": "3.2.4",
     "wait-on": "^3.0.1",