Roster: do not show contacts without mutual subscription in roster

[horazont]

Having "contacts" where the subscription state is not "both" (i.e. where either you or your contact cannot see your presence, with all what it entails) is confusing.

To make this less confusing, I propose to factor out these contacts from the normal roster, and only show them:

• If they match search terms (but sort them lowest in the list and mark them as pending) (note: tag filters are not enough!)
• In a separate window where "pending requests" can be handled. This will also help with subscription spam. A big "deny all" button would be neat, too.

In addition, we need some UI to indicate that subscriptions are pending.

[horazont]

The following states are possible:

subscription	ask	subscription received	action
none	-	false	mark as problematic, show in roster?
none	subscribe	false	show as outbound
none	any	true	show as inbound
to	any	false	mark as problematic, show in roster
to	any	true	show as inbound, auto-accept if local pre-approval exists
from	-	any	mark as problematic, show in roster
from	subscribe	any	mark as outbound
both	any	any	show in roster

• "mark as problematic": Create UI which shows possible issues with the account. Contacts which are not in fully subscribed are such issues.
• "show as outbound": Show as pending outbound in Contact Request Manager
• "show as inbound": Show as pending inbound in Contact Request Manager
• "show in roster": Display in roster (possibly with error indicator)

In addition, we should keep internal state on pre-approvals in case the server does not support them. Pre-approved contacts which send a subscription request should be approved automatically.

Things which aren’t shown in the roster by default must be shown while searching.

[horazont]

A contact management workflow has been implemented. The following is done currently:

• Contacts without full mutual subscription are shown in roster, but rendered deactivatedly.
• There is a separate management UI for inbound and outbound contact requests.

We might refine this flow later.