Use VanuatooDataGen: instrumenting/filtering data gen

- Activate through --cegis:vanuatoo
- Possibility to skip isomorphic models
- One pattern per conjunct
Improve Leon's parallel search

- Search tree can be iterated over in order
- Worker pool get displayed periodically when stuck
- Make sure global caches are concurrent
Upgrade to akka-actors 2.2.0, include configuration in the classpath
Add rule in --manual to close a branch
Reshape options, add debug sections, simplify reporters

- Debug sections can be toggled to enable detailled information
- Options can be explicitly turned off, --debug:options lists all
- Switch from multiple reporters to a single one to rule them all
- Turn cegis:gencalls on by default
Remove dependency mismatch warnings
Replacing empty finite sets should keep type information
New/Fixed testcases for oopsla
Add a couple of tests
Terminate more gracefully when manual serach is interrupted
Embed information about function closures within trees. Simpler phase.
Promote LetDef to purescala
Streamline and safeguard usage of Options body/pre/post
Remove ResultVariable, postcondition are explicitly bound
Fix the obvious insect
Implement performance regression testing

Ensures that tests run in an acceptable amount of time.
Needs at least 5 runs. Can cause failures of test-only due to
warm-up and class loading effects.
Add synthesis regression test suite

For now only synthesis tests that 100% pass. The rest of benchmarks need
to be investigated due to memory consumption issues
Remove TestUtils, don't look in innexistent directories
Timeout tests that take too long, just in case