fix tests that break under coverage instrumentation

By switching to test async code properly so instrumented code that
doesn't run fast enough doesn't incorrectly fail.

When running all the tests at once, a couple tests seem to fail
semi-regularly but unpredictably, mostly on the second and later runs.
This is the case for more tests in Chrome.
Revert "add coverage"

This reverts commit 78451242e74f9f0e0c836afa47c586c04be8deb4.
fix parsing of non-itext labels
fix intent widget references

(make it a proper plugin to avoid the circular dependency)
add test that saves and loads all question types