Added eslint. To lint, npm run lint.

Linted the entire project. Using different rules for the script files
as there are a lot of undefined variables just because of the way the
DOM's global scope works.

Mostly just code cleanup, however the linter did catch a minor bug with
a settings regex. That has been corrected.

app/assets/js/distromanager.js

@@ -483,7 +483,7 @@ class DistroIndex {
      * @returns {Server} The main server.
      */
     getMainServer(){
-        return getServer(this.mainServer)
+        return this.mainServer != null ? this.getServer(this.mainServer) : null
     }
 
 }