Updated con files reflecting that TransportDG no longer supports old TBC files.
Coefficients ad_coef, dif_coef, mm_coef defined as members of TransportDG and allocated in constructor.

This saves some time during assembly and mass balance calculation.
Test 21 for flow+heat transfer.
2D domain + fracture parallel to the flow.
Test is not included in the automated system of tests.
Fix memory leaks due to unallocated matrices.