General Speed Improvements

[bnmajor]

...there are still other places to improve. I do see extra writes to the config file, for instance.

Also, I note that when we switch chips in guided mode, we end up reading twice as many image tiles as we need -- we switch images and the tiles for the current screen location are queued, then we center the new chip and the tiles at that location are also read.

Originally posted by @manthey in #156 (comment)

[bnmajor]

Tracking some of the areas that need improvement

• Too many reads and writes to the config file (see Additional speedups #167)
• Requesting tiles twice (see Pull fewer tiles when switching view area #159)
• Moving between modes re-fetches everything every time rather than caching images
• Need to investigate infinite scroll observer (see Additional speedups #160)
• We write annotations on first load even if they didn't change
• Delete/merge hangs for a very long time (see Fix delete merge #162)