[IMP] web: do not fully hide pager in grouped view

When the list view is grouped, the page count should be hidden as irrelevant.
However if it's fully hidden, the limit can no longer be changed.
Instead of hidding the pager, this commit hides the arrows and replaces
the content by the current limit to allow to be changed.
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-linux64