Speed up Jest with changes from template project

[tpmcgowan]

• Bring over recent changes from the template project to speed up Jest.
• Remove custom test runner, jest-jasmine2 - which looks to have been added early in the project to work around a bug but is no longer needed.
• Tweak a few tests to prevent warnings about open handles being left on test runs

Performance improvements (running locally):

Before

Test Suites: 109 passed, 109 total
Tests:       598 passed, 598 total
Snapshots:   0 total
Time:        28.109 s, estimated 35 s

After

Test Suites: 109 passed, 109 total
Tests:       598 passed, 598 total
Snapshots:   0 total
Time:        7.582 s, estimated 14 s

[psoleckimoj]

LGTM