* Support multi-select during check/generate file upload
This will allow the user to select multiple YAML files via Shift-Click
or Control-Click in their browser when generating a game via the site
instead of having to zip them locally first.
* Update generate.html: File -> File(s)
* Change check.html button text to "Upload File(s)" to match generate.html
- Adjust header width for scrollbar presence
- Added new header assets for grass and dirt
- Adjusted styles for hosted and tracker
- Expand header to implement templating system
- Much more I have forgotten
