add shortcuts for Upper and Lowercase functions on plugin/editor

[malliwi88]

I added shortcuts for the functionality on Plugins/editor

Now, I will work on Widget/sourcecode/codeeditor.py for add the logic.

In order to solve issue #1669 @goanpeca

[goanpeca]

@malliwi88 please remove all white space changes to this file, its very difficult to now what change if you added cosmetic changes in all the file.

Only include the changes on the place and fix any pep8 issues next to the code you change not throughout the whole file

[ccordoba12]

Closing, as this seems superseded by #3629.