LU-1842 quota: remove leftovers from old code

LU-1842 quota: remove leftovers from old code

- remove all references to qunit_data which is the old format for
  slave-master RPCs
- gather all quota-related data structure definitions in one single
  place in lustre_idl.h
- rename lquota.h to lustre_quota.h since this is the standard naming
  scheme for all lustre components.

Signed-off-by: Johann Lombardi <johann.lombardi@intel.com>
Change-Id: Ifbadb639517c52741c210668f28452ea55bf6a43
Reviewed-on: http://review.whamcloud.com/4221
Tested-by: Hudson
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>