Set indeterminate state for facet parent checkbox only if it isn't already checked

Problem/Motivation

When displaying a hierarchy of facets, the resulting page load always shows the parent facet with the indeterminate state set when the active trail is true (i.e. when child facets are selected). However if the parent facet itself is checked, the user no longer can tell that it is a selected facet.

Steps to reproduce

• Create a facet that shows a hierarchy
• Enable the parent facet when the child is selected
• Select the parent facet and a child facet
• When the page loads, the parent facet is no longer checked and is instead in the indeterminate state

Proposed resolution

Update the selector in the checkbox-widget.js to only manipulate the parent indeterminate state if it isn't already checked.

User interface changes

The checkbox state will be different in some scenarios now.