Fix a few FFI leaks
These are instances where we obtain an FFIObject and don't call
Close on it to release the underlying reference on the Rust side.
The worst instance here was leaking an object per room member
every time we refreshed the member list
Hook up accept and decline buttons in the invites UI. Accept
will attempt to accept and then navigate to the room; decline
shows a confirmation dialog.
Fixes#106
Adds a CTA on the room list to view invites if there are any.
The invite list presents each invite with accept/decline buttons
and (for room invites) the sender details.
Fixes#102
