tracker-preferences: Fixed a number of UI issues
tracker-preferences: Fixed a number of UI issues

- Title is now "Tracker Preferences", not "tracker-preferences"
- Indexing options are now on their own page "Indexing"
- Split out the throttle and disk space limit into their own group
- Added mnemonics for notification area options
- Fixed the notification area spacing for the group.

outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker