Added optional row preference to ukernel config.

Details:
- Added the ability for the kernel developer to indicate the gemm micro-
  kernel as having a preference for accessing the micro-tile of C via
  contiguous rows (as opposed to contiguous columns). This property may
  be encoded in bli_kernel.h as BLIS_?GEMM_UKERNEL_PREFERS_CONTIG_ROWS,
  which may be defined or left undefined. Leaving it undefined leads to
  the default assumption of column preference.
- Changed conditionals in frame/3/*/*_front.c that induce transposition
  of the operation so that the transposition is induced only if there
  is disagreement between the storage of C and the preference of the
  micro-kernel. Previously, the only conditional that needed to be met
  was that C was row-stored, which is to say that we assumed the micro-
  kernel preferred column-contiguous access on C.
- Added a "prefers_contig_rows" property to func_t objects, and updated
  calls to bli_func_obj_create() in _cntl.c files in order to support
  the above changes.
- Removed the row-storage optimization from bli_trsm_front.c because
  it is actually ineffective. This is because the right-side case of
  trsm flips the A and B micro-panel operands (since BLIS only requires
  left-side gemmtrsm/trsm kernels), meaning any transposition done
  at the high level is then undone at the low level.
- Tweaked trmm, trmm3 _front.c files to eliminate a possible redundant
  invocation of the bli_obj_swap() macro.