add metadata information and UI switch to study test errors vs test failures

[monperrus]

In Junit:

• A test failure is a test that does not pass due to an exception that extends AssertionError (or maybe Error, to be verified)
• A test error is a test that does not pass due to an unexpected exception that does not Extend AssertionError.

In order to be easier for people to select the ones containing failures and/or errors, what about adding a filter on the test problem (error vs failure)?

(My assumption is that it's a different task, probably easier, to not throw an exception than to satisfy a set of assertions)