Gravity Perks - Live Preview 1.6.12

Improved support for Gravity Forms 2.5. (#9)

- Added full support for Gravity Forms with improved UI.
- Updated CSS for hidden fields in Gravity Forms 2.5
- Fixed issue where admin script was not output when No Conflict Mode was enabled.
- Fixed issue where tooltips displayed underneath the form editor toolbar. Fixes #5.
- Removed tags in selectors.

Added gplp_grant_preview_permission filter to allow filtering whether the current user has permission to preview forms via Live Preview.