Add app packager

[andydotxyz]

So we can create apps that better meet the expectations of a GUI user.

macOS: create an app bundle
windows: insert required metadata

Can we extract the icon set on the app object to avoid re-stating what is already coded in?

[niaow]

Also:

Linux: generate packaging scripts and /usr/share/applications entry. See this for more info.

[andydotxyz]

That's the macOS support in the feature/package branch. Need to add Windows and Linux before we can merge in.

[andydotxyz]

(for now using command line parameters rather than trying to parse the app's metadata from Go)

[andydotxyz]

First pass linux is added @jadr2ddude, though I used /usr/local though - /usr is for system apps :).

Not sure about the resulting .tar.gz but without OS specific metadata it seemed like the most appropriate thing to do.

[andydotxyz]

Windows support now added too :)