CRM-16504 fix recurring option to show on membership renewal

CRM-16504 fix recurring option to show on membership renewal
This patch also moves a lot of template code that is shared between the backoffice
membership renewal and the backoffice membership receipt. From what I can tell the rest of the
file could pretty much be shared code and I think there is some invoice functionality
missing from renewals as I spotted a case where there was an invoice related class
on the member form but not the renewal (that is now in the shared code)
I also found (& fixed) a situation where the amount shows for people with membership but not contribution
permissions. It is now suppressed like other contribution fields

The next step towards bringing these closer is to use the same email field name on both.

In fact the templates look for either {receipt_test_signup} or {receipt_text_renew} so
it makes sense to just set {receipt_text} - although that involves a change to the msg
template so I don't know how off-putting that is