GMail-app-style generated colorful one-letter contact pictures for pictureless contacts
Changed hash based color calc to a hash indexed palette as discussed in the pull request.
Bugfix for negative modulo result indexing the palette array
Caching also the calculated anonymous bitmap as proposed by maniac103. This removes a lot of code for special handling unknown contacts.
Added more finer characters as proposed by cketti
Fixed NPE found by blackbox87 ... thanks pal!
Using Android proposed colors as contact color palette now: http://developer.android.com/design/style/color.html
Changed the fallback char from 'K' to '?'. The riddler was here ;).
Merge pull request #353 from sfuhrm/gmail-style-user-pics

Gmail style user pics, 2nd try

* sfuhrm/gmail-style-user-pics:
  Changed the fallback char from 'K' to '?'. The riddler was here ;).
  Using Android proposed colors as contact color palette now: http://developer.android.com/design/style/color.html
  Fixed NPE found by blackbox87 ... thanks pal!
  Added more finer characters as proposed by cketti
  Caching also the calculated anonymous bitmap as proposed by maniac103. This removes a lot of code for special handling unknown contacts.
  Bugfix for negative modulo result indexing the palette array
  Changed hash based color calc to a hash indexed palette as discussed in the pull request.
  GMail-app-style generated colorful one-letter contact pictures for pictureless contacts

Conflicts:
	src/com/fsck/k9/activity/misc/ContactPictureLoader.java
	src/com/fsck/k9/fragment/MessageListFragment.java