Refactor preloading for current dates

This is a cleanup version that has reviewed many components and simplified the data structures for the History and Preload utilities. The options pop-up was worked on to simplify the code and a small "Saved" indicator was added when settings are changed instead of just closing the window. A few more tests were added including full coverage for the History component. Also some old CSS was chopped out from the old vanilla JS version.

It might not look like much, but under the hood it feels good.