Bug 911247 - Extract the link from a message and make it clickable r=julienw

- Message contents are now parsed and specific fields extracted
- The messages are now stored as parsed objects into a dedicated
  IndexedDB store instead of as raw text into asyncStorage
- Dismissing the application is supported correctly including when the
  view activity is invoked after clicking on a link. As a consequence of
  this attention screens are not used anymore
- Tests have been added to cover most of the functionality
Merge pull request #12254 from gabrielesvelto/bug-911247-wappush-url

Bug 911247 - Extract the link from a message and make it clickable r=julienw