Flip and rotate toolbar options

[manongjohn]

A requested port from T2D which will add the following:

• Selection Tool Flip and Rotate Buttons
  

• Animate Tool Flip and Rotate Buttons

• Shortcuts for new Flip and Rotate buttons

• Behavior of buttons:
  • Flip Selection/Object Horizontally: Multiplies H value by -1
  • Flip Selection/Object Vertically: Multiplies V value by -1
  • Rotate Selection/Object Left: Adds 90 to rotation value
  • Rotate Selection/Object Right: Subtracts 90 from rotation value

[manongjohn]

Linux build failures due to something with the Linux build environment and not related to these changes. May be a transient thing with Ubuntu archive where it gets packages from. Someone can try restarting the builds later.

[F-Burning]

Thank you!

I was looking for the rotate icon on the bar, and the flip option to the selection is very useful.

[RodneyBaker]

@konero has mentioned via discord that he will add the missing icons involved in this feature set to his list.

[RodneyBaker]

Will press forward with this PR as although the Mac runner should be working again it isn't essential for buildiong the nightly release.

Thanks @manongjohn for the feature port/code!