Change labelClass from function to property

[jbourassa]

Getting labelClass from the template would output the stringified version of the function, because it wasn't a computed property. This fixes it.

[Emerson]

Looks like this is the same issue as #25 - I'll see what I can do this weekend.

[igorrKurr]

I believe you need to change ember-qunit version to 0.4.1 here - https://github.com/Emerson/ember-form-master-2000/blob/master/bower.json#L9. Maybe other dependencies also should be updated, so you can find good example here - https://github.com/jgwhite/ember-sortable

[jelhan]

@Emerson What blocks merge of this small fix? fm-radio-group isn't really usable without this fix. It looks like this (taken from dummy app):

<label class="function labelClass() {
      return this.fmconfig.labelClass;
    }">Choose the best language</label>

[jelhan]

Addressed this issue in #36. Was the same for helptextClass in fm-helptext.