smarter default file name for deck downloads

[tooomm]

Make the default deck name something like:
gamemode_timestamp or date_localtimestamp_gamemode, not sure if other informatin like playercount would be too helpful

So a filename could look like: 2017-04-23_17-21_sealed.txt or 2017-04-23_draft_17-21.cod (with the timestamp at the end)

The idea is get a useful filename which you don't have to change all the time, which isn't overwriting other files and actually provides useful information!

Edit: Even more important... just realized that the name is also baked into the .cod file and therefore shows up if you load the deck file in the deck editor, plus it can't really be changed there by the ordinary user:

  <deckname>16-04-2017_3</deckname>

[dev-id]

Fixed by b848a15

Default is now format-date-time.ext. Overrides cookie though.

Also date/timestamp is server time I think.