minSdkVersion to 9 (gingerbread)
initial gradle build
gitignore .idea and build
support content uris for key files
fix key file selector to work with kitkat
simplify dirty tracking

Will result in refreshing more, though a bit more obviously correct (and
not missing any necessary refreshes).
cleanup direct access to groups and entries in PwDatabase

Still not quite sure what is going on with #groups vs #getGroups(), but
it's a start.