Make payment instrument required for all contribution, event registration and membership forms

1* Modify the Payment Instrument option value edit form (e.g. civicrm/admin/options/payment_instrument?group=payment_instrument&action=update&id=82&reset=1) to expose the Default? (is_default) field to admins.
2* Modify xml/templates/civicrm_data.tpl to set is_default TRUE for 'Check'
3* Add upgrade code to set is_default TRUE for 'Check'
4* Payment Instrument required on Contribution ADD and EDIT forms
5* Contribution ADD form should set Payment Instrument default to is_default payment instrument value.
6* If API for contribution op==create (ie add or update) receives parameters that do not include a value for Payment Instrument, then ensure the default is used (NB: is it possible to use BAO to set default values and call that provide defaults fn from Contribution Add form and during API call to create contribution? This would be a good general pattern.)