Prepare test suite for upcoming fixes and improvements.

Clean separation between SQL tests (which should apply to both Web SQL and this plugin) and plugin-specific tests.

Add reproduction of minor bug #204.

Move reproduction of #209 to section with plugin-specific tests.

Mark some plugin db tests that were added by Mark Oppenheim (mailto:[email protected]) as "Needed to support some large-scale applications".

Test repeatedly open and close db two ways (whether or not to wait for open callback before closing db)

Add another test of repeatedly open and delete db (wait for open callback before deleting db)

Needed for #184/#204/#209/#210/#211/#213.