Broken off from COMPASS-291 and should be implemented after that.

Show a modal popup to warn the user when they try to run an empty explain {} because that is potentially very expensive on the database and we already know the result: a collection scan.

Acceptance Criteria:

• When the user enters an empty query (or uses the default empty query) and hits apply, a modal window should appear with a warning text and 2 buttons, cancel/continue. Only when the user presses continue should the explain be executed.