FloatArrayLoader: correct float type

This was supposed to be referencing the ImgLib2 float type, but was
mistakenly pointing to come.sun.jdi.
FilterTest: manually register filters

We shouldn't rely on annotations on test classes. For this filter
discovery test, the filters are now manually added.

The annotations themselves still remain for constructing new PluginInfo
instances, but that should be refactored away eventually.

Closes #79