[New Feature] Use long press to change center freq and center mark

[GoogleCodeExporter]

Use long press to change center freq and center mark. It's son uncomfortable to 
change freq pressing buttons a lot of times, instead it would be nice if the 
user could press and hold a button pressed and it keeps changing freq while 
it's pressed down.

See links below in order to get further information:

1) 
http://stackoverflow.com/questions/5253371/play-sound-while-button-is-pressed-an
droid

2) 
http://stackoverflow.com/questions/2615616/triggering-event-when-button-is-press
ed-down-in-android

3) 
http://developer.android.com/reference/android/view/View.OnLongClickListener.htm
l

4) 
http://androidforums.com/application-development/17033-ontouch-onlongclick-toget
her.html

Original issue reported on code.google.com by zz4...@gmail.com on 23 Feb 2012 at 11:02