Debug memory issues with Valgrind

[Michael Schlottke-Lakemper]

As part of my efforts to fix #39, I ran a valgrind check on HOHQMesh using valgrind ./HOHQMesh -test. This resulted in some memory leakage (~64 KiB), but more importantly in several, usually non-negligible memory errors:

• Conditional jump or move depends on uninitialised value(s): >= 3 times
• Use of uninitialised value of size 8: > 20 times
• Invalid read of size 8: > 20 times

In my C++ experience, the errors are seldom something one can safely ignore (the leakage is only troublesome when one actually runs out of memory because of it; at the moment I wouldn't worry too much about those). Thus it might be good to put some time into trying to fix the hard errors, especially in light of the increased activity lately.

cc @DavidAKopriva @andrewwinters5000