WPML String Translation Support +

- Passed variable through the GetText function when outputting so WPML String Translation can catch it.
- Changed 'widget-title' to 'widget_title' to conform to previous convention.
- Perform a str_replace to change the '_' to '-' in order for the 'widget_title' to appended to the collapase widget field instead of regular 'title'
The reason this is required is because 'wp-admin/js/widgets.js' specifcially looks for the first element with an id ending with '-title' so '_title' won't work.
Source: https://core.trac.wordpress.org/browser/tags/4.0/src/wp-admin/js/widgets.js#L391
- Added Image and New Window options as optional fields making 'widget_title' the only Mandatory field.