Adds fieldset functionality

- Fieldsets allow the display of multiple fields that save to the same
  meta key. Right now the display implementation is the only one working
- Unit tests probably fail all over the place
Working: saving fieldset data

- Fieldsets for text fields now works correctly in both render and validation
It works!

- Validation and binding of existing data to fieldsets now works.
- Fieldsets enabled for standard input fields and select fields
Adds some validation error handling

- no longer will attempt to validate a url field if the field is empty
Fixed, improved tests

- Most test failures were bugs in the code fixed in /inc/meta-box- models
  and view
- Most errors were due to changes in the data implemented in the code
- ToDo: Add tests for fieldsets, with this commit, coverage will likely fall
Merge pull request #1 from gboone/fieldset-feature

Fieldset feature