Implement better naming scheme for work threads.

This commit changes the way work threads are named. Work thread name
now contains indication whather the action is reader or client related,
the action code and the reader label or client username.

{{{
Thread name:
  w[r|c]XX-[rdr->label|client->username]

Fields:
   w      - work thread prefix
   [r|c]  - depending whether the the action is related to reader or client
   XX     - two digit action code from enum actions
   label  - reader label or client username (see username() function)
}}}

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8298 4b0bc96b-bc66-0410-9d44-ebda105a78c1