Now passing submitted files to the DomainGlobalSettingsForm so that user uploaded logos will be saved

`self.request.FILES` was not being passed to the `DomainGlobalSettingsForm`. As a result, the logo was never set on `self.cleaned_data` and the conditional black at `commcare-hq/corehq/apps/domain/forms.py:302` (where the logo is set) was never being entered.

Will resolve http://manage.dimagi.com/default.asp?120034