Move an animation to a specific frame

[stanmots]

moveToFrame public function makes it possible to move an animation to a required GIF frame. It works according to the following algorithm:

1. Stop currently played animation;
2. Extract GIF frame in accordance with the given index;
3. Display this frame;
4. Rebuild the cache (animatedFrames array) during the next animation starting procedure.

[kaishin]

@storix Does this still depend on #38? In which order you prefer them to be merged?

[stanmots]

@kaishin No. #38 is deprecated. You can review and merge this PR completely independently now.

[kaishin]

Ditto #42 (comment)

[kaishin]

Will reopen to keep track of the feature.

[rk85097]

Any plans on adding this functionality? I really need it :)

[kaishin]

@rk85097 No concrete plans, but if you want to look at the PR as a reference and make the changes necessary in the current version that would be terrific.