CON-1809 | Fix overlapping of anchored element

@vforge You put big part of the logic in private helper methods and call all on them in the one which is exposed `handleLinkTo`. This makes writing unit tests to these methods impossible. On the other hand when looking at these helper methods logic it seam a right to move them to separate modules:

- getting elements offset - separate DOM utils module which will be used across site or jQuery if we already decided on using it
- sanitizing href - use `wikia.querystrig`
- pushing to history state - different module responsible for history management

All this modules should be added as dependencies which will make them easy to mock in unit tests. if you go with this approach than you will have only one function in this module - `handleLinkTo`. I'd suggest changing name to for example `scrollToTarget` or something more descriptive. in tests for this method you will check if different methods from modules in dependencies were called with appropriate parameters and if this method return appropriate values based on the params passed to it as arguments.