#1788 Alert users if Editor pane is minimized

[Jean-Christophe Helary]

Some OS window settings trigger a minimization of all the panes in OmegaT.
Users who are not used to OmegaT think the project has failed to load and do not know how to handle the issue.

OmegaT should test the state of the Editor pane and send an alert to the user with the possibility to reinitialize the pane layout.