Organize build scripts into build-aux

[grillo-delmal]

Just thought that reordering the build scripts might help the repo to look neater. I basically created a build-aux folder and organized all the build helper scripts inside there.

@orowith2os suggested this to me on #272 for the files in that commit, but here I expanded it to the whole repo.

I'm just following my own compass on this, so feel free to close it if you don't like it or if you think this is unneeded.

Here is a more exhaustive list:

• Created a ./build-aux folder
• Moved build specific stuff from ./res/flatpak/ to ./build-aux/flatpak/
• Moved windows specific build scripts from ./ to ./build-aux/windows/
• Moved osx specific build scripts from ./ to ./build-aux/osx/
• Moved linux specific build scripts from ./ to ./build-aux/linux
• Moved translation helper scripts to ./ to ./build-aux
• Fixed workflows to find scripts in their new home. Nightly result on this branch

Best regards and keep up the good work!

[orowith2os]

Noting that the Flatpak desktop file can be moved to be used for all Linux stuff, as the executable is the normal binary and will be changed when the Flatpak builds it.

AppImages also aren't provided anymore, is res/AppRun still needed?

[LunaTheFoxgirl]

It is not, more cleanup needs to happen + I need to get around to make a WIX installer for Windows.