Format as code

[raineorshine]

• Add a new command and toolbar button to wrap the thought in <code>...</code> tags.
• Use an icon from the Noun Project that looks like <>. Make sure it is positioned, sized, and styled consistently with other toolbar buttons.
• Use a similar isActive method as bold, italic, underline, strikethrough toolbar buttons.

  em/src/shortcuts/bold.ts

  Lines 20 to 25 in ee9b4ba

  	isActive: getState => {
  	const state = getState()
  	if (!state.cursor) return false
  	const thought = getThoughtById(state, head(state.cursor))
  	return thought.value.includes('<b>') || thought.value.includes('<strong>')
  	},

• When part of a thought is selected, activating the command should wrap the selected text in <code>...</code> rather than the full thought, and set the caret to the end of the selection