Lizzie Version 0.7.4

This update contains all the pull requests over the last year or so that @kaorahi merged today.

Changelog

I'll compile the full changelog later, but from @kaorahi's post we have at least the following:

• Fixed many bugs.
• Much improved diagnoses of engine troubles. (#677, #747, #759)
• Added new features by @yzyray and @TFiFiE.
  • #650 on subboard...
    • mouse hover to stop flicker
    • mouse wheel to change variation length
    • left/right click to show nth variation
  • #656 grayscale territory (toggled by Shift+Period key)