Add evaluate action (Ctrl-Alt-Enter) button to the toolbar

The button is only visible when a Python Editor is active (i.e. in the same
conditions as when Ctrl-Alt-Enter would do something.
Merge branch 'development' into pullrequest/add_evaluate_action_to_toolbar
Merge branch 'pullrequest/add_evaluate_action_to_toolbar' of https://github.com/jonahkichwacoders/Pydev into jonahkichwacoders-pullrequest/add_evaluate_action_to_toolbar
Merged: add evaluate action (ctrl+alt+enter) to toolbar.