Replaces file_match field with a user set conditions which applied

will be tested on all posted review requests for the corresponding

repositories.
Changes:


Removed file_match field from form


Added Conditions widget to form


Added description field to form and as a list column


Added diffed file options (corresponding to old regex functionality)


Added evolution for database


Refactored code for adding default reviewers to a ReviewRequest


Added lazy migration for default reviewers


Migrated when tested against review requests


Migrated when before being edited by an admin

Created a test repository with a test struture to try various

conditions including string matching and files diffed.
Created commit to trigger migrations and be applied to review

request.
Test commit as review request to verify expected behavior 

before applying evolution
Applied evolution
Posted review request to verify same behavior was exhibited
Test other string operations

ends with
starts with
contains