Store private keys for pseudonyms and restricted groups in the DB.

...et/sf/briar/android/groups/WriteGroupMessageActivity.java

briar-api/src/net/sf/briar/api/db/DatabaseComponent.java

briar-api/src/net/sf/briar/api/messaging/LocalAuthor.java

briar-api/src/net/sf/briar/api/messaging/LocalGroup.java

briar-core/src/net/sf/briar/db/Database.java

briar-core/src/net/sf/briar/db/DatabaseComponentImpl.java

briar-core/src/net/sf/briar/db/JdbcDatabase.java