Cleanup: fix most 'unused parameter' warnings

Cleanup: fix most 'unused parameter' warnings

... and several bugs hidden by lack of this check:

* url_rewrite_timeout parser/dumper using wrong cf.data.pre
  parameter definition.

* url_rewrite_timeout parser/dumper using wrong object for
  state data.
  Global a Config object instead of parameter object.
  Preventing future use of multiple Config objects. There is
  more to be done as the Timeout value itself is not stored
  as part of the object apparently detailing the timeout.

* request_header_add directive dump() omitting directive
  name in mgr:config output.

* dead code as HTCP packet handlers for NOP, MON, SET

* mime icons download operation incorrectly initialized.
  was using the 'view' access parameter to set download
  access permission.

* peerCountHandleIcpReply() assertions testing validity
  after pointers already used. This would lead to segfault
  on errors, now leading to assertion logging.

Only the default built code was checked and updated at this
time. There are 62 known warnings still appearing due to
parameters being only used inside conditional code, possibly
more issues in code not enabled in this build and certainly
a lot more in the stubs and unit tests which were not checked.