Some context menu changes for the main tree view

[LukeUniverse]

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Added a few options to the right click context menu for the TreeView on the left hand side of the screen. New items I added:
Move up to {Previous Section}
Move down to {Next Section}

Collapse all
Collapse {Current Section}

Add: {CurrentSection}

Where Current/Previous/Next Section is replaced with the text of the that section such as "Sounds" "Tile sets" "Sprites", etc etc.

I also rearranged the MenuItem_*** methods to be alphabetically ordered. Which has created some visual clutter in this Pr which I probably should have avoided >.< oops, hah. First time trying to do a PR on github, so I guess I'm learning. hah