Generalized export of linear system solvers

- This is initial commit for this work.
- Idea is to implement custom lin. sys. solver with QR (at least), for
cases m >= n;
- Added customization for the number of backsolve steps, <= n.
Updated Householder QR based solver and found a bug

- The solver works for A with dim nRows >= nCols
- Fixed a bug related to the case w/o reuse feature
- Disabled export of the solver in case reuse it TRUE, until bugs are
  fixed
- Added calculation of determinant, the solver return determinant of
  matrix R now.