Links: Various improvements

* Avoid an API hit to show the target language card. Use the information
  from the link adaptation for the section (adapt API call when a link in
  source section clicked removed)
* Cache the API requests for getting the link information.
* Simplify the start method of the module. Removed lot of redundant
  and unwanted method calls from the time of single-card design.
* Associated minor code clean ups.

Change-Id: I1a020ec050f0cb30c01b9feaa81a6a65daab0ced
Merge "Links: Various improvements"