preferences: added quiet-while-charging

Adds a setting 'Quiet While Charging' that disables ringing
and vibrating while the phone is plugged in.  This is
intended for people who plug their phone in at night and
don't want to be woken up.
Merge pull request #32 from jeffkaufman/quiet-when-charging

preferences: added quiet-while-charging
android: RevizedEditPing activity to handle rowid=0 by returning list of tags.
android: Added Beeminder related databases and initial implementation of goals
list
android: Implemented goal editing and link to Beeminder
android: Finalized GUI to add/update/delete goal links and tag associations
android: Tuned up strings and goal list view
android: Documented EditPing and fixedbug when going home from EditPing
android: Started implementing an IntentService to handle Beeminder communications and datapoint management
android: Implemented point creation and deletion (database only) for ping edits
android: Implemented actual point submission and proper thread synchronization
android: Minor fixes
android: Worked on point deletion mechanics
android: Notification on errorduring deletion or creation
android: Implemented error handling for protocol mismatch
android: Error handling and retries
android: Added delayed retries
android: Finalized retries, giving up and better handling of datapoint deletion
android: Implemented goal time to filter datapoints and pings
android: Used session reopen instead of close/open for more efficient thread use