Fixes #1534, #1518, #1716, #1618, #1450: Refactored repeating motions

[Chillee]

I did a lot of refactoring of the repeating motions. I initially did it to try and fix gbb and surround easier, but it turns out that our current system is actually unsound. It relies on the order that @RegisterAction pushes actions into the list, which we have not specified any guarantees about.

I also switched gc and gb around, for two reasons. For one, gc is the actual keybinding used by the commenting plugin. Number two, gbb is not a sound keybinding. Are we executing gb over the range of b? Or are doing the gcc command?

Yes, I realize that this might screw up what some people are used to, but I think it's worth it, for the philosophical soundness :)

As per discussion with @johnfn, I added an annoying error message everytime somebody tries to use "gb" or "gc", as well as a setting to disable those messages. The plan is to have those annoying messages until a couple weeks later, when we can remove them.

In the process of refactoring the repeating motions, I also fixed some other isssues (and another regression actually).

Fixes #1534, fixes #1518, fixes #1716, fixes #1618, fixes #1450.

[Chillee]

I think this is another PR that's ready. Only controversial part about this PR is the swapping of gb and gc. However, I've added a loud Error notification when the user uses any of the 2, saying that gb and gc have been swapped, as well as telling them that there's a setting that disables it.

I think we should merge this PR sometime and then push a release. Or maybe we can sneak in that neovim change too :^)