Animated Preview

[Seth]

I can’t open a pull request so this is the next best thing

I wrote up some simple code to cycle through the rendered previews in `m_Fractorium->ui.SequenceTree;` giving a nice animation of the sequence. I recorded a video demonstrating this feature

The code is here: https://github.com/sethtroisi/fractorium/pull/2

There are several commits in the PR that fix various compiler warnings and one that fixes includes on my system. (Ubuntu 20.04)

The final two commits (https://github.com/sethtroisi/fractorium/pull/2/commits/4f7dfa614798f33be2ca5e05f0e3cc1a11f396f5 and https://github.com/sethtroisi/fractorium/pull/2/commits/84d033c99a776c0dbf1ca0c99dc510fc5656218f) Implement the feature.