Autodetect blender executable on linux.

[Leha44581]

Linux has a handful of default filepaths to all executables, or to be more specific their desktop entries under $HOME/.local/share/applications, /usr/share/applications, or /usr/local/share/applications, im sure there's others im not aware of.
It would be nice if i didn't have to manually specify the filepath to it.

[ColinTimBarndt]

It would also be possible to search for a blender executable on the PATH