Bug 544155: [History Editor] Add option to remember answer to "add to history" prompt

Add information to the dialog about what package(s) will be added
to the history, and include a "Remember my decision" option.
Add a preference page to clear "Remember my decision" dialog answers.

Change-Id: I63ba794d7b14959819a63881690e1035733e8269
Signed-off-by: Christian W. Damus <give.a.damus@gmail.com>
7 files changed