also adding wrapper for the backwords step

this commit does not work, the generalized EVP problems fail from 2
reasons:
- Cannons algorithm does not work for the processor grid shape we use at
  the moment in tests (It only works if num. of process columns is a
  multiple of num. of process rows, which is not true in ELPA for 2 mpi
  tasks)
- Cannons algorithm does not work as integrated to ELPA for larger
  matrices (not clear why at the moment)

There are 2 new tests, which should work
- test_cannon.c: it tests the new algorithm without going through
  Fortran, as it has been delivered
- test_c_bindings: it tests transfering a 2D fortran matrix to C and
  back, as it is done with the cannons algorithm in the normal ELPA
  tests

- per default only some tests are run
- by setting CHECK_LEVEL=extended all test jobs are run

To be used like this

   class(elpa_t), pointer      :: e
   class(elpa_autotune_t), pointer :: tune_state

   e => elpa_allocate()
   call e%set(...)
   [...]
   assert_elpa_ok(e%setup())

   tune_state => e%autotune_setup(ELPA_AUTOTUNE_FAST, ELPA_AUTOTUNE_DOMAIN_REAL)

   ! Autotuning loop, continues until all combinations have been tried
   do while (e%autotune_step(tune_state))
     ! Do the steps that are representative of your calculation
     call e%eigenvectors(a, ev, z, error)
   end do

   ! Fix best parameters, and de-allocate the autotune object
   call e%autotune_set_best(tune_state)
   call elpa_autotune_deallocate(tune_state)

matrix for the test not prepared (called with zero matrix)
list of gitlab tests temporarily reduced

adding variants for single precision and complex math datatype
for the scalapack test

test analytic has been transformed to template to allow all
real/complex and single/double variants. However, at this
commit, only real double and real single variants are enabled

yet another attempt to improve single/double and real/complex
unification more readable

with obvious meaning

for easier comparisons of elpa and mkl, a test case using scalapack
function pdsyevd has been added