Signature actions enabled while account still loading

[danirabbit]

What Happened?

When the account is still loading we get an empty signature dialog and buttons don't do anything

Steps to Reproduce

1. Kill mail and restart it
2. Open the signatures dialog while mailboxes are still loading
3. Notice that buttons don't do anything until accounts are fully loaded

Expected Behavior

We should have some kind of indication that things are still loading and disable any actions that won't work until loading has completed

OS Version

8.x (Circe)

OS Architecture

amd64 (on most hardwares)

Session Type

Secure Session (Wayland, This is the default)

Software Version

Early Access or Compiled from git

Log Output

Hardware Info

No response