Add hotkeys for text formatting in Markdown editor

Description

When I type some text in the editor, it's not very useful to move my hand to grab my mouse just to click to a button to format text.

Proposal

Add hotkeys when focus is in the Markdown editor (md-area):

Action	Suggested hotkey	Current status
Toggle Write/Preview	CTRL + SHIFT + P	Implemented
Add bold text	CTRL + b	Not yet implemented
Add italic text	CTRL + i	Not yet implemented
Add inline-code text	CTRL + c	Not yet implemented
Insert a quote	CTRL + >	Not yet implemented
Add a task list	CTRL + u or CTRL + o	Not yet implemented
Add a link	CTRL + k	Not yet implemented