[FIX] calendar: dropdown button misaligned

+ add meaningful placeholder
[IMP] Cleaning of reporting (group_by, filters), adding new favourites and default views, some renaming (py and xml files)
[IMP] test_inherit: add test case, redefine Many2one field in inherited model
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32