Solitude facade for pay providers (bug 987903)

There was an old universal provider API but it was
half baked and assumed that we would hide the details
of Bango behind Solitude. This new approach allows
for Bango to be unique while making room for
"standard" providers if we get them.
Merge pull request #408 from kumar303/unipay

Solitude facade for pay providers (bug 987903)