Fix Nuxeo 6.0 TestThemeStylingService tests

nuxeo-6.0-fullbuild-jdk8-daily is failing with these errors
https://qa.nuxeo.org/jenkins/view/6.0/job/6.0/job/nuxeo-6.0-fullbuild-jdk8-daily/70/#showFailuresLink

• org.nuxeo.theme.styling.tests.TestThemeStylingService.testStylesRegistration
• org.nuxeo.theme.styling.tests.TestThemeStylingService.testUnregister
• org.nuxeo.theme.styling.tests.TestThemeStylingService.testFlavorsRegistration

The same errors can be seen when doing a T&P on the branch 6.0 when using Java 8. The tests pass with Java 7.

The errors about the theme (TestThemeStylingService) are caused by an order problem: the print and default styles are retrieved in different orders. This is due to the use of HashMap instead of LinkedHashMap in a few places, and HashMap iteration order has changed between Java 7 and Java 8.