Separate out XML files for preference categories

Actual ~code~ doesn't work yet of course
Integrate all settings files into current prefs system

All loaded as PreferenceScreens by SettingsActivity.
Trigger preferences (image settings etc.) still spawn their activities too
Reorganise SettingsActivity into menu sections with separate calls

Each screen's setting initialisation, summary setting and callback methods
are grouped together. Hopefully it'll be easier to add stuff and make
fragment/multi-pane magic happen later, or at least split it out into
components
Remove member refs to preferences

Goodbye members, hello local temps. Only used for setting listeners anyway
Clean up summary-setting algorithm

Summaries that use Entry values can use those nice loops someone put in
Convert About dialog to use a string array
Group Settings menu strings in strings.xml

Rearranged everything that's used in each screen, all in one place now
Reword some settings menu text
Organise everything in strings.xml

Well ALMOST everything. There's things to be deleted too
Change ... to ellipsis characters

Hey if you're offering. Thanks, android studio!
Split out last sections and add HC+ pref checks and summaries

Import/Export are now in a separate XML file, there's a method to create
section dividers, and API-dependent prefs are handled programmatically
Set defaults and enables to "false" in XML

They weren't disabling in 2.2, so disable by default and let the code
enable them on later APIs.
Also added a flag to prevent summary setting code being called before
the Preference hierarchy was loaded (happened on new installations thanks
to onPreferenceChange kicking in)
General preference reorganisation

Also set a dependency for 'only load images on wi-fi', so it's only
enabled if 'load images' is enabled - makes sense to me, but maybe people
want full control so they don't spend some data pennies, I don't know
Fix XML defaults and force 'off' values with code

Defaults are set once and universally, so I put them back to the 'normal'
defaults and forced them off in the code itself. So now all checking and alt
default setting is done in SettingsActivity
default
default
Null check for external storage

Crashes emulators without SD cards, might be fine on all devices but worth
catching at least
Lots of text rewriting and general settings shuffling

Rewrote and reorganised names along the style guide lines. Lots of things
needed shortening for the tiny babby screens, and also some of my names
were bad and are hopefully now less bad
Make P2R summary show current value, finish text rewrites
Niceify the account features summary

Put some tabs in there
Add current value summary to Thread Layout pref

Tablets can actually use this huh? Let's help them out
Also changed the Hardware Accel text to make it one-line on a GNex,
could be shorter though?
Write some documentation and delete unused files