Add configurable list view of contacts

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Show list view of contacts, either on the new dashboard or in the side panel

With other chat clients like Groupwise Messenger or Pidgin I'm used to having a (configurable) list of contacts providing an overview of which people are working today / available right now / etc.
I consider that really helpful and much easier to use than having to look up people individually via the search field.
A business use case might be looking for some contact person in a certain department without choosing an individual person beforehand.

Now that we have the new dashboard page for Talk, maybe adding such a list there could be an option.
For better handling, a few filter options - everybody, certain user groups (departments), those in state "online", those marked as favorites, ... - would be good, preferably multi-selectable to combine attributes, e.g. "group xyz" AND "online".

As an alternative this could also be placed in the sidebar, although that might not be unfeasible because of the rather limited space available there. Or it could be implemented as another dedicated page similar to the "home page" / dashboard.

Each entry in the list should provide a means to directly start a personal chat.

[Edit: more detailed description]

Start by reviewing the Talk dashboard, sidebar, and existing contact search flow mentioned in the issue. Determine which location can support a configurable contact list and combined filters. Done means users can browse contacts, filter by the requested attributes, and start a personal chat directly from an entry.