Rich time-relative content in !submit DM response

[jakethedev]

The bot should respond smartly via DM for submit command usage, instead of the current "welcome" response in-channel. Something like
"Thanks for submitting to #server's battle! There is X TIME remaining for submissions, $flavortext"

Where $flavortext is a random choice in certain arrays. Pick the array by how much time is left.
Under 30 minutes: [ come up with fun ones for this ]
Under 1 day: [ general "hey nice work / good timing" messages ]
Over 1day: [ there is still X amount of time left, so if you want to update your submission, just run the !submit command with your new link, and you'll get a new confirmation message ]

Relates to #67 - could be a nice two-part overhaul