Bug 835793 - Fix errors in the list of modules supported by Fennec
- Updated `widget` as unsupported module
- Added `page-worker` and `system` as supported module
- Added Flavored MD syntax for deleted content (~~)
- Updated `sdk-docs.css`
- Removed comments from `mobile.md` to make it more readable
- Removed the changes on markdown parser
Added missed modules (plus index-db)
Merge remote-tracking branch 'upstream/master' into mobile-doc-fixes/835793
Fixed typo on indexed-db
Merge pull request #747 from ZER0/mobile-doc-fixes/835793

Bug 835793 - Fix errors in the list of modules supported by Fennec