This is an initial attempt at making the reduced credit feature use individual dates for sets.

- The reduced credit feature is now turned on and off in course config.  If its off then options relating to it are not shown.
- The reduced credit period in course config is now a default period.  I can be overridden in the set detail page.
- The reduced credit percentage is now a percentage select.
- The reduced credit date is kept in the database and this commit will require a db upgrade.
- The reduced credit date upgrade has an associated pg pull.  In particular the way the reduced credit graders work had to be changed since the reduced credit logic was built into them.  This may break custom graders that use the old reduced credit logic.

- I also added an option in the config area which enables or disables conditional release, and will hide the options relating to it.
- I upgraded conditional release so it cannot be "hacked" using the url.
Make it so that conditional release and reduced credit are enabled by default.  We may need to change this for master.
Made it so that the system doesnt check for conditional release if conditional release is disabled.
Fixed a small bug where sometimes the config select would save a label instead of the value.
Merge branch 'develop' of https://github.com/openwebwork/webwork2 into reduced_credit_date
Changed a lot of the reduced credit's to reduced scoring's.  I may have missed some and I didn't change the localization tags on purpose since that opens a can of worms.
Changed the default reduced scoring state to 0.
Changed conditional release so it is defaulted to off.
Reverting a change that really should be in release/2.9
Added reduced credit field to UserDetail page.
Added datetimepicker functionality to the reduced credit date.
Merge pull request #341 from goehle/reduced_credit_date

This looks good.   

Reduced Credit Date (develop)