A crash could occur if the plugin window was closed and reopened and a
new resource was added to either the Variable, Action queue, Websocket,
or Twitch tab.
No context object was provided to the signal handlers.
The signal provider is intentionally not deleted when the UI is closed.
Because of this, the signal connections were never cleared when the
underlying tab widget was destroyed.
So, in the case of closing and reopening the settings window, the old
connection with the outdated widget pointers would be called again.
The order of operations was incorrect.
First the signal that a variable was removed was propagated before the
variable was actually selected.
So e.g. scene item selections would receive the signal that a variable
was deleted but when repopulating the scene item selection the variable
still exists resulting in the list of available entries not to change.
This should make it significantly easier to get an overview of the
variables, which currently exist, modify their settings, or potentially
remove multiple variables.
* Remove could lead to the "add" dialog being opened
* Rename could result in some entries not being renamed (due to
FilterComboBox using a QComboBox with setEditable() set to true)
