Adding support for Python3
* Moved launcher from Edit menu to Tools menu
* Added method for plugin deactivation
* Sorted languages by their full name instead of their ID.
* If the user changes the name or ID, it now saves it as a copy instead of overwritting the original file.
* New schemes are now saved to the ~/.local/share/geditstyles/ directory
* Made it such that the "Clear" button is disabled when there are no style attributes for an style item.
* Catch and get rid of exception for when a language has no styles.