* Break CSS into modules.
Drops the compile test by 3 KB.
Remove obsolete .blocklyDraggable class stub (it used to be dynamically changed).
Remove unused menuseparator CSS.
Random improvements to require statements.
Removal of some obviously dead CSS.
.blocklyDropDownDiv no longer supresses text selection (see comment in PR).
This PR drops the compiled size by 4 KB, which is larger than I was expecting.
