Foreground image + transparency + fixes

[fsobolev]

Main:

• [x] Ability to set foreground image (Closes #86)
• [x] Ability to set transparency for background and foreground images (Closes #85)

Other:

• [x] Update Aura (Closes #111)
• [x] Update CAVA in flatpak and snap (Closes #103)
• [x] Switch back to using Pulse Audio by default (Closes #100)

[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 https://github.com/NickvisionApps/Cavalier/pull/112/commits/024089f6daa2dea5fbbff5e1ac1f0d0e4782daf7

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.