[Widget] Menu based on group permission

Development
2 
<script type="text/discourse-plugin" version="0.8">

    var u = api.getCurrentUser();

    if (u !== null) {
        u.findDetails().then(function (u) {
            if (u.groups.some(function (g) {
                return g.name === 'MyGroupName';
            })) {
                // User is member of the group
            }
        });
    }
</script>

This will incur in an extra network request for .findDetails but works.