Installer: Re-use ResourceLoader methods instead of duplicating

Also:
* Fix incorrect documentation comment of ResourceLoaderModule::getStyles(),
  it doesn't return a string, it never has.
* Remove spurious space in count() call.
* Fix spelling of in "proper".

Change-Id: I000393636f7b9015ad1bacfbb3eb8a6ad8695d72
Merge "Installer: Re-use ResourceLoader methods instead of duplicating"