Extract screen painting stuff into a separate struct

[nixypanda]

From #62 > #62 (comment)

Extracting the Painter seems to absolute clean up some clutter and makes changes to output code centralized. Full endorsement from my side.
Future thought: Maybe the Painter could also do the bookkeeping on the terminal positions regarding where the current prompt started/where the current offsets are (in this case maybe named TerminalOutput) (need to be called on resize)
With a good design it is probably reasonable to hand out exclusive references of the Painter to (plugin) components.

[sophiajt]

I like the refactor - this should help a lot

Had a comment about making sure we use the cached terminal size, but other than that I think this should be ready.

[nixypanda]

@jonathandturner made the change you asked for.

[sophiajt]

Looks good!