Foreground image + transparency + fixes

[fsobolev]

Main:

• Ability to set foreground image (Closes Suggestion: foreground image instead of color (transparency gradient?) #86)
• Ability to set transparency for background and foreground images (Closes Suggestion: Colors on either side of "splitter" #85)

Other:

• Update Aura (Closes Update Aura to 2023.9.1 #111)
• Update CAVA in flatpak and snap (Closes Update to Cava 0.9.1 #103)
• Switch back to using Pulse Audio by default (Closes Can't connect to audio #100)

[nlogozzo]

Also, po and pot needs updating

[nlogozzo]

Did you want to fix #99 and then make this rc1 and stable friday?

[fsobolev]

Did you want to fix #99

Sorry, forgot to make a separate commit, it was fixed in 024089f

make this rc1 and stable friday?

I want to make this beta1; rc and stable next week. Considering the amount of changes I want to give more time for people who want to test it.