Implement `vec_dense_matrix_eq_perm`

This function checks whether two vectors containing dense matrices are
equal upto a permutation. This is essentially the same function as
`vec_basic_eq_perm` in src/dict.cpp with minor modifications to be used with
dense matrices and was implemented following a suggestion by Isuru.
Refactor `test_homogeneous_lde` to use `vec_dense_matrix_eq_perm`
Add new tests
Add the source of the first two tests
Merge pull request #339 from thilinarmtb/homogeneous_lde_tests

Tests for `homogeneous_lde`