Add keyboard shortcuts for formatting tools

Objective:
* Add keyboard shortcuts for paragraph, heading 1-6 and pre-formatted

Testing:
* Using [control+num] triggers appears to work well on Chrome, Safari, Firefox and Opera on Mac

Changes:
ve.init.Target.js, ve.init.mw.ViewPageTarget.js
* Add formatting commands to targets
ve.ui.MWFormatTool.js
* Add mediawiki specific format tools and commands
ve.ui.CommandRegistry.js
* Add commands for all formatting tools
ve.ui.TriggerRegistry.js
* Add triggers for formatting tools

Bug: 33512
Change-Id: I5d6176eff50aa3cea72aed226ca06512629412d4