Circlevis

* show all four keys in the visualizer
* adjusting mods now changes all related values (AR, OD, CS)
* fix rare out of bounds crash when retreating frames at the beginning of a replay

* fix `VisualizerApp` error on start
* cap slider steps to avoid ridiculously long sliders hanging

* add `Visualizeron_load`
* add `Classifiervisualizer` hook

* add `Visualizeron_load` method, which is called when the visualizer finishes preprocessing of the beatmap, replay, sliders, etc and is ready to display gameplay
* this is a no-op and is intended to be overridden by subclasses to perform actions that require a loaded visualizer (eg, seeking and taking a screenshot of the visualizer)

* fix error when trying to draw judgments for replays with no beatmap available
* move speed up and speed down controls to the left of the timeline scrub bar, and copy to clipboard to the right
* add `Classifier` class for quickly classifying batches of replays. See https://github.com/circleguard/circlevis#classifier for more details
* move misses below snaps and edge hits in the events table
* only preload replay statistics if there are <= 5 replays
* add shortcut (`,`, `.`) for retreating or advancing by a single millisecond respectively
* rename `pause` to `toggle_pause`, `force_pause` to `pause`, and `force_unpause` to `unpause`

* fix errors when visualizing multiple replays
* fix spinners always being marked as misses