[sailfish-browser] Rebase text selection feature to latest master

This is an experimental patch enabling the text selection feature. It depends on the latest code in xulrunner and qtmozembed available in :next and is not supposed to be merged to mainstream.

Note:
1. text selection may not work on some sites (e.g. mobile.twitter.com);
2. the code doesn't use system info banner, but its own implementation;
3. the draggers implemented as circles of fixed size looks weird when selecting lines of text of different font sizes.