Feature Request: Include Themes in Exports & Make Backup Solution

**Is your feature request related to a problem? Please describe.**
I lost **all** my custom themes when I switched to a new system - because I thought a theme is precious user data which will of course be backed up. I still get sad when I think about the lost time investment (I had 6 custom made themes with several hours of work - perfectly adapted to low-res LCD - Screens) - and I still hope that I'll find them somewhere I copied them to but forgot about.

**Describe the solution you'd like**
⮱ Add a Checkbox »Themes« below Configuration & Commands in the Export - Dialog.
⮱ Add a info text which tells the User what data wil **not** be included in the export/backup.

**Describe alternatives you've considered**
Promote copying the config folder as backup - solution.