Mouse keyboard controls

[bnmajor]

This adds a new component that contains a summary of the available mouse and keyboard controls. The component takes a prop to indicate if it is mounted in the setup or predictions step. If mounted during the setup step a few additional controls are listed (that are unavailable in the predictions step):

• The annotations category:
  • Left-click: Label single superpixel
  • Shift-left-drag: Continuously label superpixels
• Under the Pan category:
  • Arrow keys / Shift-arrow keys / Shift-ctrl-arrow keys
• Under the Zoom category:
  • Plus, minus / Shift-plus, shift-minus / Shift-ctrl-plus, shift-ctrl-minus
  • 1 - 7: The number keys 1 - 7 will zoom to discrete zoom levels.
• Under the Rotate category:
  • <, > (also . or ,) rotate the image a small amount. If shift is held down, < and > rotate the image 90 degrees.
  • 0: 0 returns the image to the default orientation.

In all cases the container is collapsible so that the text can be hidden if preferred

Closes #73

[jeffbaumes]

From the screenshots this looks great from a functionality standpoint.