Allow opening multiple files when launching

[ThomasWilshaw]

After completing #123 it was suggested it would be good to implement loading multiple files at launch. I've attempted that in the following way:

On launch check if the first file presented contains a wild card and if so attempt to open all files in the given directory that have the same file extension. If the first file does not contain a wild card, try top open all files presented.

This seems to work pretty well but could do with a bit of testing, especially on none Windows platforms as there is always path weirdness to contend with.

Examples:

// Open a.otio, b.otio, c.otio
raven.exe a.otio b.otio c.otioz

// Open all otio files in current folder
raven *.otio

// Open all otioz files in specified folder
raven path/to/my/folder/*.otioz