Extra features: Improved/Added commands to match Github, Added line/lines duplication/movement

[RARgames]

Hey,

Here is a list of the main changes:

• Enhanced ALL default command buttons (e.g. bold, italic, list) to match Github behavior (e.g. include remove feature)
• Added table, mention, issue, help commands
• Added Ctrl+D to duplicate line/lines
• Added Alt+UpArrow/DownArrow to move line/lines
• Other minor fixes

Feel free to review and select features that you want.