Issue #65: Export only non-default field settings.
Issue #65: Add support to edit AttributeTable & Edit widget field date settings.

* Use field settings internally when preparing layer settings.

* Order user-defined field settings.
Issue #65: Disable editing of layer field names.
Issue #65: Add support to reorder fields from layer settings.
Issue #65: Clean up.
Issue #65: Rename fieldItem to fieldSettingsOption.
Merge with develop.
Issue #65: Update AttributeTable layer settings pop-up to support field date settings.
Issue #65: Fix duplicate variable warnings.
Merge branch '#65/support-date-field-options-in-attribute-table-and-edit-widgets' into develop