[GUI][Bug][Trivial] Console not showing output text when changing the wallet theme

[ambassador000]

1. Start the wallet with Dark Theme
2. Type any command in the console
3. Switch from Dark to Light theme
4. Command output is not visible anymore as well as the white text above "Welcome to the PIVX RPC..."
   

Additional:

1. Run the wallet with Light theme
2. Type any command in the console
3. Switch from Light to Dark theme
4. Command output will be visible, but with the different text color
   

[random-zebra]

Yes... both issues have the same root.
The stylesheet change in QTextDocument is applied only to to newly inserted text.
Old text is unchanged (so, e.g., white text becomes invisible when switching from dark to light mode).

I don't think there's a convenient QT function to repaint a QTextDocument with new stylesheet directly (@furszy ?).
Maybe the best solution is just to clear the console area, when the theme is changed, and re-write the "welcome" message (so at least the new style is applied to that).

[furszy]

A bit delayed answer but here.. just commented in #2236 (comment) .