Summary:
Currently, `ManiphestAuxiliaryFieldDefaultSpecification` uses about a dozen giant `switch` statements to implement stadard field types (int, string, date, bool, select, user, remarkup, etc). This is:
- pretty gross;
- not extensible; and
- doesn't really let us share that much code.
I got about halfway through porting a similar implementation into StandardField but I wasn't thrilled with it. Subclass StandardField instead to implement custom field types.
Test Plan: Added an "int" custom field, verified it had integer semantics and indexed into the integer index.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D7005
