Colorize info window when transcribing

[Enyium]

As I described in #73, transcription can sometimes be triggered too easily, at least in "continuous" "Recording mode". And when WhisperWriter is transcribing, it can (at least currently) not also record. This means that it would be useful if the info window would be colorized, so that just seeing it in your field of vision makes it salient enough to communicate that, if you started talking now, not every part of your speech would be recorded.

Imagine you have a writing app open and are lost in your thoughts. WhisperWriter is in "continuous" "Recording mode" and was triggered to listen. You only bring out a sentence every now and then and are thinking much. If you accidentally trigger WhisperWriter to start transcribing using some non-speech sound, you have to wait until it's ready again. And this shouldn't catch you by surprise or annoy you and push you out of your thoughts by only capturing half of your speech. If the info window would customarily have a different color during transcription, you could easily learn to harmonize with accidental transcriptions (that don't produce output when using the VAD filter).

On the technical side, the info about the necessity to colorize would probably need to be injected into BaseWindow.paintEvent() (including a call to Qt's repaint() method?).