Remove warnings from test cases

[sgleizes]

In every test case using the Wicket Tester, the old method startComponent(Component), which is deprecated, is used.

We should replace it by startComponentInPage(Component).

Stephane Gleizes

[hielkehoeve]

Most testcases are still from the Wicket 1.4 era, feel free to totally change them or replace them.

I have mostly tested all components in our applications, as these are much better test cases than a small bit of Java code.