Initial migration to navigation drawer and Fragment

- Migrated I2PActivityBase and subclasses to Fragment
- Added new MainActivity with navigation drawer to handle Fragments
- Added MainFragment to navigation drawer

Code compiles, installs and runs. Known bugs created:
- Some buttons now fail (can't use an Intent with a Fragment)
  -> Migrate usage of Intents to Fragment transactions
- New install/upgrade dialogs are commented out
  -> Migrate old Dialogs to DialogFragments
Removed "I2P Home" from action bar (linked in navigation drawer)
Moved Fragments to net.i2p.android.router.fragment

Side-effect: some constant strings are now public
Enable app icon for navigation drawer opening
Fix labels in navigation drawer
Migrated home buttons to use Fragment transactions
Removed unused imports
Fixed static reference
Converted AddressbookActivity to Fragment
Load WebFragment properly from AddressbookFragment
Only call onBackPressed for I2PFragmentBase subclasses
Renamed menu1.xml
Moved Addressbook button to navigation drawer
Use dp instead of px, added content description for logo
Show some menu items in action bar
Set choice mode for navigation drawer

This should have enabled the current navigation drawer entry to be highlighted
by the call to setItemChecked() in selectItem(), but it still doesn't work.
Migrated old Dialog to DialogFragment
Removed unused imports
Show navigation drawer on first run
Turned navigation drawer code into base activity to subclass