Remove 'undefined' from notes
Update JSON with timestamp

I've added support for a timestamp to be automatically generated in
json.html. The column is added to table view, but hidden by default as
no games have dates yet.
Change edit link to json.html

json.html enforces consistency because it autogenerates. it also has
further, more detailed instructions for adding to the file and adds the
timestamp automatically.
Remove commented note from when table view was broken.
Always show steam url, even if a key isn't provided

Some games have a steam url defined even though the game isn't listed as
giving out a key. In this case, show the link as usual, but fade it out
and set title to a warning to indicate a key is not provided.