Tested against W3C web-platform-tests

Tested against the multiEntry and compound key tests in
web-platform-tests for indexedDB.

A lot of bugs was corrected to make IE11 pass the W3C unit tests for
these features.

However, one unit test in Dexie failed after the corrections, namely the
upgrading: updgrade test. Need to debug that and see what's happening.

Also, still havent implemented deleteIndex or deleteObjectStore