Updated shortcuts

[HeCorr]

Somewhat related to #1016 / Fixes #1444.

This PR removes the following unused shortcuts:

• Export Sound (Ctrl+I)
• Preview (Alt+P)

..and adds the following missing shortcuts:

• Export Animated GIF (Ctrl+G)
• Toggle Center Overlay
• Toggle Thirds Overlay
• Toggle Golden Ratio Overlay
• Toggle Safe Areas Overlay
• Toggle One Point Perspective Overlay
• Toggle Two Point Perspective Overlay
• Toggle Three Point Perspective Overlay
• Import Image Predefined Set
• Import Movie Video
• Import Movie Audio
• Import Animated Image
• Import Layers from project file
• Import Palette (Append)
• Import Palette (Replace)
• Toggle Range Playback
• Peg bar Alignment
• Lock Windows
• Reset all tools to default
• Change Line Color (Current keyframe)
• Change Line Color (All keyframes on layer)
• Selection: Reposition Frames
• Change Layer / Keyframe Opacity

Please let me know if I've missed any!

[HeCorr]

The View > Preview (Alt + P) action/menu item/shortcut seems to be unused as well. Should I go ahead and remove it?

If so, should I also remove the (seemingly abandoned) preview.cpp file?

[MrStevns]

Nice job HeCorr!

I'd recon that we remove the preview file for now, since it's been lying there for a long time and never gotten fully implemented but maybe @chchwy disagree?

[chchwy]

Nice job HeCorr!

I'd recon that we remove the preview file for now, since it's been lying there for a long time and never gotten fully implemented but maybe @chchwy disagree?

It's totally fine to remove it for now. It should be added back once the feature is fully functional.

[HeCorr]

Preview feature and it's shortcuts removed!

I found some more missing shortcuts to add and also some that don't match their menu name:

Menu name	Shortcut name
Reverse Frames Order	Selection: Reverse Keyframes
Remove Frames	Selection: Remove Keyframes

Should it be Frames or Keyframes?