ditch useless PgpKeyHelper.getMasterKey methods
more work on streamlining uris, and stripping ProviderHelper
db-overhaul: more work on new provider

specifics:
 - secret keys are preserved when a new public key is inserted
 - started work to give virtual columns a representation in the contract
   class
 - streamline ProviderHelper methods. the getUnifiedData method relies
   on a api level 11 method, not sure yet how to fix/workaround that...
 - many more small things work as they did before
db-overhaul: minor stuff, mostly ProviderHelper
db-overhaul: reintroduce by-mail and by-subkey queries

the only thing left to fix after the db upgrade (that I can think of
right now) are key exports
db-overhaul: fix loading indicators in KeyListActivity and ViewKeyActivity
calculate nfc packet on demand only
db-overhaul: different hack for type info (api level problem inside)
Merge remote-tracking branch 'origin/master' into db-overhaul
db-overhaul: workaround api level 11
db-overhaul: fix DecryptAndVerify with and without known keys
ViewKeyMainFragment cleanup (don't use inline queries!)
db-overhaul: fix delete key from ViewKeyActivity
db-overhaul: fix key export (and some export-related ui changes)
Merge remote-tracking branch 'origin/master' into db-overhaul
Merge pull request #513 from Valodim/db-overhaul

Get everything working again after db overhaul