Merge tag '2.0.0' into develop

Most of the classes have been refactored to be easier to maintain
Library usage now works differently (see https://github.com/Rudloff/alltube-example-project)
Various download bug fixes
Accessibility improvements (thanks to @hiwelo)
Fixed tests running on CI
Updated youtube-dl to 2019.04.24

package.json

@@ -1,7 +1,7 @@
 {
   "name": "alltube",
   "description": "HTML GUI for youtube-dl",
-  "version": "1.2.5",
+  "version": "2.0.0",
   "author": "Pierre Rudloff",
   "bugs": "https://github.com/Rudloff/alltube/issues",
   "dependencies": {