Compute residuals recursively

Conflicts:

	fishtest/fishtest/views.py
Fixes
Bad users had residual 0.0 after first pass, fix that
Add purge run button
Do not hardwire blocked users in fishtest

Use a file for this.
Remove only worst user in calculate_residuals

From:

https://github.com/glinscott/fishtest/issues/26
Remove only worst user: take 2

See comments on:

https://github.com/glinscott/fishtest/commit/8be8f4c9a6d12ba7ddf64bb5
Merge pull request #2 from glinscott/master

Merge