Service requests page: allow to save table column widths

This is to address the following error:

ActionController::RoutingError
(No route matches [POST] "/miq_request/save_col_widths")

https://bugzilla.redhat.com/show_bug.cgi?id=1145140
Merge pull request #618 from mzazrivec/miq_request_save_column_widths

Service requests page: allow to save table column widths