Describe the bug
When a user enters fullscreen mode using the "Enter Fullscreen" action in the menubar, the text does not change.

Expected behavior
I would have expected the text to change to "Exit Fullscreen". Otherwise there is no action displayed to exit fullscreen mode.

Steps to Reproduce
Open a PyDM window with the menubar enabled, click "View" in the menubar, click "Enter Fullscreen", click "View" in the menubar again, and notice that the action is still labeled "Enter Fullscreen".

Possible Solution
In the file pydm/main_window.py, we can change the function PyDMMainWindow.enter_fullscreen() to also update the name of the action that calls it:

• file: pydm/pydm_ui.py
• property:Ui_MainWindow.actionEnter_Fullscreen
• function: actionEnter_FullscreensetText()