Calculator: Prevent pasting in TextView in lockscreen widget

Pasting on a RemoteView requieres the use of the new getBasePackageName included in API 18.
Otherwise, the addActiveOwnerLocked will be launch a unhandled Security exception.
This changes remove the copy/paste/cut actions from the TextView when API is lower than 18.

Change-Id: I53f4743f69c1490854017863a1bc2324b2d47034
JIRA: CYAN-882
Issue: https://jira.cyanogenmod.org/browse/CYAN-882
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>