Data is now by default cached in sessionStorage and not localStorage.
Can be configured via the "storage" option.

Also fixed 2 bugs.

1. Instead of checking whether minimized chats toggle is visible, check whether
there ae aleady minimized chats (visuals might be delayed).
2. Don't call restore from removeChat. Chat gets restored earlier.

When a chat is minimized in trimChats, trimChats needs to be called again (in
case the minimized chats toggle is newly shown).

Debounce the "restore" method to avoid breakage due to double click.

Still rough around the edges

Instead of differentiating between trimmed chats and minimized chats, the two
are now combined into the same thing.

This commit contains some initial work, but functionality is still impaired.

of any existing ones, but left of the control box.

* Make sure that a restored (grown) chat is inserted to the right
* Make sure restoring via the contacts roster works