Translating thread and wait to js and test harness for multi-threaded programs

[zilinc]

This PR fixes #218 and supersedes #219.

It includes changes in the following aspects:

1. It changes the JS test harness (test/harness/testharness*) to newer versions from the upstream WPT repo. This is required because it fixes several problems around fetch_tests_from_workers and tests getting stuck (which also affects the upstream WebAssembly/spec repo).
2. It fixes the JS test harness to support Either expected results.
3. It implements the generation of the thread and wait constructs in wast scripts.
4. It allows the test harness (test/harness/async_*) to work with multi-threaded test cases. It includes the JS file names under test in the test reporting, because otherwise the test harness will complain about duplicate test names coming from different threads.
5. It also fixes several race conditions in the JS test harness that are not only present here, but also in the upstream WebAssembly/spec repo (main branch). For instance, in the assert_unlinkable function, it does not wait for the preceding updates to the registry to happen. It will non-deterministically produce wrong test results (false negatives and false positives) depending on the timing and order of the tests.
6. Updates to the build scripts (test/build.py) with additional flags. (In the upstream WebAssembly/spec repo, it generates some JS file in the wrong paths, resulting in non-existent files when running the testsuite; but this behaviours is not present in this branch of this repo.)
7. With all the fixes, there're still several failed tests in the testsuite due to the differences between production web browsers and our interpreter. Chrome and Firefox give the same results. The failed tests are:

test file	# failed tests
import.wast	6
global.wast	4
elem.wast	4
binary.wast	16
data.wast	4
memory.wast	4
threads/atomic.wast	2