Default install stanza

[pjf]

While thinking about #112, it struck me that we could make a default install process which looks like this:

• Search for the top-most directory with the same name as the mod identifier
• Copy that directory into GameData
• But not .ckan files
• And also not Thumbs.db files (if we decide we don't like them)

This could trigger for a standard (not virtual) package that's completely missing an install stanza. It would cover the vast majority of simple mods, and would also avoid mistakes like I made with DogeCoinFlag where I can't spot the route to my own directories.

Topmost directory means we handle things like GameData/MyMod/assets/MyMod/foo.png correctly.

[pjf]

Working on this now, because it's going to make everyone's lives much, much easier.

[pjf]

This also fixes a bug where we crash the GUI if we try to view
a module that has no install stanza. :)

(Although we'll need to address that separately for virtual packages,
as they'll never supply files by themselves.)