* remove references to basestring & unicode (use relevant pycompat
helpers)
* remove some str calls (either entirely or replaced by relevant
helper, either text or native)
* use better API to avoid unnecessary conversions
* remove some XML declarations in views
After modifying the database schema, if some models do not have a table/view,
attempt to recreate it by calling their method `init()`, following inter-model
dependencies.
Fix the model `board.board` by making it an abstract model.
Add the missing model dependencies on report `crm.partner.report.assign` to make
it depend on report `account.invoice.report`.
Xavier Morel