finalize a “dark mode” ace editor theme

[pq]

ultimately, editor modes should be consistent w/ the upcoming maiden re-styling (#63). in the meantime, a proposed dark mode, based on ace “tomorrow night” is in flight (#121).

this issue is a place to discuss refinements. (we could consider a companion to discuss a light counterpart that is in the spirit of #63 but since i prefer dark, i'll let someone else spearhead that... happy to help though! 👍)

the (default) vs code dark theme might make a good source for inspiration. see:

• VS Code Theme Color Reference
• vscode/dark_plus.json at master · Microsoft/vscode · GitHub

see also: #33