Don't crash when startActivity() fails

Fixes issue 6201
Change message body font size with slider, using new setTextZoom() WebView API, from 40% to 250%
Fix display error in account settings

* correctly initialize summary of 'Server search limit'.
* don't persist value in shared preferences
Save/restore slider state
Merge pull request #448

Change message body font size with slider
Merge remote-tracking branch 'upstream/master'