Update matfaust LazyLinearOp.

- Add is_meth and refactor check_meth.
- Fix ctranspose.
- Fix mtimes: handling scalar mul and don't create a LazyLinearOp if multiplying a dense matrix or a vector (evaluate the calculation).
- Fix full: if the result of evaluation is not a dense matrix, call full.
- Handle arbiratry number of input arguments in cat, horzcat and vertcat.