Fix sporadic travis test failures

Some ContainerTest unit tests could fail depending on the order the tests were executed. The problem is that Xerces maintains a global table with counts of registered listeners in org.apache.xerces.dom.LCount, so if a test method that does not properly unregister its listeners, it may influence the behavior of subsequently executed tests.

The fix unregisters all test listeners at the end of each test and adds missing event listeners where they are necessary for the expected behavior.
Conflicts:
	core/src/test/java/de/betterform/xml/xforms/ContainerTest.java
FIX: removed 10% chance of parseISODate() failing when parsing xs:dateTime values

xs:dateTime as implemented by Saxon does not pad the
fractional seconds with zeroes, leading to a parsing error
in ExtensionFunctionsHelper.parseISODate whenever the
time to be parsed contains a number of milliseconds
that is divisible by 10. As a consequence, the unit test XFormsExtensionFunctionsTest.testNow() failed in approx.
1 out of 10 executions.

This patch fixes the parsing function and tests the
modified behavior.
Merge pull request #35 from opax/travis-fix

Improve stability of unit tests