docs: fix testing instructions for installed build
fix number of returned values for no refinement in refine_reference()
fix make_l2_projection_data() for parameter variables
fix path in script/gen_lobatto1d_c.py

- bug introduced in ec186b8c69b0719f483e11a864092a21a608a203
clean up script/edit_identifiers.py
fix sys.path in auxiliary scripts and standalone examples

- for cases where the current directory (i.e. top level sfepy directory) is not
  added automatically