installation: pip requirements

• Adds requirements files for Pythonic prerequisites, taken from the master branch, modulo some unnecessary dependencies.
  
  Useful for Python-2.6 based installations of maint-1.0/maint-1.1 branches. (Note that the maint-1.0/maint-1.1 branches shall remain Python-2.4 compatible.)

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>