Add license support

[alexgleason]

Erwin's collection just got license support. The json output now contains a "license" key in SPDX format. It would be nice to see that metadata added to this viewer. Thanks!

[felipemanga]

While the desktop builds generally have enough room for more metadata, the Android and browser builds need to be compatible with small screens. As is, the description window is really cramped on phones and needs work before I can add anything else.

Also, since you can easily see a game's license by using its source link, the information is easily obtainable to those that want it.

[alexgleason]

I think displaying the license on desktop and hiding it with a media query could work. This is what GitHub does on repos.