More flexible and customizable ReportHandler situation

[zkat]

The default reporters are fantastic, and there's even hooks to customize them with, but you're kinda stuck with the overall look beyond what the GraphicalTheme provides.

It's not ideal for everyone using miette to have "the miette look". It should be possible (and easy!) to piece together your own handler while still taking advantage of the fairly complex snippet and such reporting code.

This might also involve merging the graphical and narrated handlers into two modes of one big handler (maybe even include #29 in that). Also all the logic for switching between them and figuring out some terminal specific things.