[WIP] Single entry in lightbox

[zackkatz]

Most of the work is being done on includes/extensions/lightbox/.

To enable:

1. Add a "Link to Single Entry" field
2. Open field settings
3. Check the "Open in a lightbox?" checkbox
4. Save the View

Big things to work on

• [x] Allow for Next/Previous and Single Entry navigation options.
• [ ] Remove single entry widget header hooks add_action( 'gravityview/template/before', array( $this, 'render_widget_hooks' ) ); (started work here: class-gv-request-rest.php Request::is_entry())
• [ ] When "open in lightbox" is enabled, disable "open in new window" option.
• [ ] Remove the <— Go back link
• [ ] Add setting to enable/disable indexing of single entry pages when opening in a lightbox.
• [ ] Make sure to embed Custom CSS and Custom JS output.
• [ ] Edit Entry isn't working.
• [ ] Enable galleries inside modal

💾 Build file (5f5499e08).