Converts ConferenceUrl to a class and binds an instance to the global
APP variable, as requested by HTerezov.

Is not very readable and is not used across the project

We need to make sure that on the page reload all original parameters
used to load the conference are preserved. New modules helps to manage
different types of conference URLs like the one used for invites and
the one for reloading the page.

Remove check for the call overlay being visible in postponing
the toolbar being hidden, as we don't want to have it displayed at all
when the overlay is there.

Will disconnect on ConferenceErrors.VIDEOBRIDGE_NOT_AVAILABLE.
Show the same message when either JVB is not available or Jicofo
disconnects.

Fixes issue of method 'setTooltip' in modules/UI/util/UIUtil.js: Excluded 'Uncaught TypeError':
```
UIUtil.js:134 Uncaught TypeError: Cannot read property 'setAttribute' of null
```

Uses some ES6 syntax. Also removes inputHeight key for resolution as it makes no sence to have dictionary with one key. Removes some code duplication. Makes code consistent: method params for updateLocalStats and updateRemoteStats.