Add the ability to save and replay traces generated by invariant violations

[emichael]

Remaining TODOs before this is merged:

• [x] Save and replay traces on a per-lab basis
• [x] Allow the choosing of a specific trace through run-tests.py
• [x] Allow the replay of a trace with the visual debugger
• [ ] ~Consider making --save-traces the default (probably not a great idea) and if it is, update the README~
• [x] Make sure traces are only saved on invariant violation (and not missing a goal)
• [x] Add tests to the tst-self directory that all of the basic StatePredicates are serialized/deserialized/cloned properly and that the trace object does the same
• [x] Add name of test/class failed to SerializableTrace, print it out when replaying
• [x] --no-save-traces in grader.py looks wrong

Additionally, once this is merged:

• Clone lastSearchSettings in BaseJUnitTest on the feature/new-visualizer branch

[emichael]

Merging this is now blocked on merging https://github.com/emichael/dslabs/tree/feature/unique-test-numbers