Terminal output for subprocesses inside Dodo

[The-Compiler]

As discussed briefly in #63, it's easy to miss errors that happen in subprocesses (e.g. offlineimap), or lose useful debugging information if not running in a terminal (e.g. sendmail or gpg failing).

That information should probably be part of the UI. A first proposal of how it could work:

• Dodo has a statusbar widget, which (among potentially other things, like match count?) could have some icons or text-equivalent on the bottom right for subprocesses it runs.
• For long-running subprocesses, it could show [sync], [sendmail] etc. while the process is running. For things that are expected to complete ~immediately, that probably wouldn't be shown to avoid things getting too busy.
• When a process completes, its marker disappears (or is greyed out). If it fails, its marker shows up as red.
• Clicking said marker opens a small terminal window in the UI (should be doable with a read-only QTextEdit, I have something similar in qutebrowser) that shows its output. Maybe it could even open automatically on failures.

It's a bit unfortunate that this will involve quite a bit of complexity, but IMHO it'd be worth it anyways. Not going to work on this immediately, but I might take a look sometime in the future. Thoughts?