Add rank tracking to matches

* Add columns to matches table to store start and end ranks for players
* Record the start ranks for players when match is created
* Record the end ranks for players when match is completed
Fix player profile display

There was an issue with the player profile listing new players as
available for challenges because their ranks are 0. The
'within_challenge_range' method now checks if the base_rank should
be calculated or 0.
Fix bug with scheduling_info in challenge email

This bug was intruduced when switching to responsive email
templates.
Merge branch 'master' into add-rank-tracking-in-matches