Enable more collab UI features (#3496)

* Current Call section of the collab panel
* Improve the collab titlebar
* Add basic UI for following

Following only partially works, but the UI for following is now in
place.

Cargo.lock

@@ -1222,7 +1222,6 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "async-broadcast",
- "async-trait",
  "audio2",
  "client2",
  "collections",
@@ -1242,9 +1241,7 @@ dependencies = [
  "serde_json",
  "settings2",
  "smallvec",
- "ui2",
  "util",
- "workspace2",
 ]
 
 [[package]]
@@ -11534,7 +11531,6 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "async-recursion 1.0.5",
- "async-trait",
  "bincode",
  "call2",
  "client2",