Gizmo manipulation via touch: Improve position / rotate / scale gizmo use on touch devices

[tracygardner]

• Add on screen buttons when gizmo is active, mapped to keyboard commands for gizmos

[lawsie]

#668
Add touch controls for axis-based gizmos

[lawsie]

#670
You can now switch between touch/keyboard/mouse modes for axis gizmos. Buttons made clearer with colour labelling and thick border for selected axis. Only the axis you are moving on is coloured during translation.

Move gizmo now displays properly with world axes not object. Buttons are also context aware and will display different directions for X and Y/Z axes making movement clearer.

[lawsie]

• Various small bug fixes #673
  Bug fixes for gizmo manipulation on touch screen devices.

• Hud Y rotation bug #688
  Fix bug where Y rotation using HUD didn't work properly. Prevent uniform being selected for rotate/move gizmos.

• Bugfix - rotation gizmo slider  #690
  Rotation slider bar now updates block value and slider position correctly when bar is clicked. Rotation is from -180 to 180, the slider now reflects the initial position correctly. Snap marks at 90 degree angles have been added to aid positioning

• Add show-hide button for gizmo HUD #727
  Add button to Show/Hide the gizmo HUD. Preference remembered between gizmos.

[lawsie]

• Add Eye gizmo #691
  Add 'eye' gizmo to orbit mesh (same as V keyboard shortcut), uses 0 on gizmo overlay. Syncs with same option in the context menu on a block.