digital: fixed psk and qam constellation table generators. Not sure how these got out of sync.
qtgui: adds menu item to clear max and min hold lines on frequency plot.
qtgui: fixes problem of set name not showing up.

Defaults to blank string now; a blank string does not set the title to save vertical space. Any other value will now set the title of the plotter.
qtgui: changed all examples to start wtih empty name fields.

Don't want to have QT GUI Plot show up for every plot now.
Merge branch 'maint'