Store expired state within ImportKeysListEntry
First version of automatic contact discovery.

TODO:
- Configuration (much of it)
- Enabled by default?
- Which keys to import? Current state: All non-revoked and non-expired with matching userid
- Search for keys if already known? Current state: yes, may cause traffic (configuration: only when wifi?)
- Update interval: Currently Android handles it, might be good (causes automatic refresh on new contact and stuff like that) or bad (too many of refreshes)
Fix regex for hkp parsing to support multiple uids