init  invoice_opportunity model
add opportuntiy to invoice detail page
add xls export
1, select 'closed/won' opportunity (of invoice' account) features to invoice detail page. use '*' to list all opporuntiy or type text filter.

2, in opportunity page, associate opporunity to invoices (that belongs_to opportunity account). if opportunity doesn't belongs to account. no invoices in selection.
add invoice group into account detail page,
note, 'Select Invoice' has no effect, as  for account page, you can only create/delete/edit , can not  discard and select invoice for account.
fix opportunity invoice select. only can  select from account's invoice list