Fix error with refreshRate other than 5000

Would throw some NullPointerExceptions and caused the app not to work.
Wrapping it inside a null check seems to do to the trick.
Improve language
Remove unnecessary variables
Improve SettingsController

This commit replaces saveSetting by saveSettings, as currently the save
method is only called from one place anyways, which saves us a few
duplicate checks.

Also moved the path + filename to a private class attribute, as this
doesn't change anyway in between two method calls.
Lower sleep time on the saveVibranceSettings thread.

Ten seconds seemed a bit too long, because if you opened the application,
changed a setting and closed within 10 seconds the changes weren't saved.
Remove commented isVcInstalled

Now that the project is inside git, there should be no reason to
not remove commented code. When you want the method back, you can simply
revert this commit!