Don't show git related files in the editor

Add '.git' to blacklist
Fix file save and upload and improve security

Integrating file save and upload to fs class and removing their respective action files.
The file save and upload mechanisms got broken in recent changes to file handling, this commit fixes them.
Adding previous and next tab actions

Adding keyboard shortcuts and menu actions for selecting next/previous tab.
Updating tabs library to support these actions, and doing small changes and improvements to the whole library.
Improving the way keyboard shortcuts are generated to the menu items.
Other small improvements to menu and tabs.
Small misc improvements

Fixing menu items not centered.
Changing the 'unsupported file types' bug description.