This commit only renames things, changes no logic. Any mention of "book", "view", or "mode" is renamed in relation to "spreads".
The AnchoredBox.jsx file is renamed to Anchored.jsx
Extra icons are deleted, and the remaining ones are renamed.
the `-alt` icons have better sizing/readability than the originals. The originals likely will be removed.
Also adds back in 'fit-width' icon which was mistakenly overwritten earlier.
Removes icons as components, uses mask-image instead.
Sets a size on the .fac icons to 1em so by default they are 1em and retain their aspect ratio.
rename the icon files for consistency.