Treat frequencies in bookmarks as 'LongLong' (qint64)

Fixes issue #192
Merge pull request #193 from mrenouf/master

Read bookmarked frequencies as int64
Increase max screen width to 16k pixels (issue #203).
Add 2.5 Msps preset for Airspy (issue #212).
Update news info.
Update version numbers.
Update about dialog.
Merge branch 'v2.3.x'

Conflicts:
	gqrx.pro
	news.txt