Searching for HippoBean's can only be done currently by defining a primary nodetype, which does not have the option to search for subtypes of the HippoBean

We should for example be able to search for all HippoBean of type HippoDocument bean. Currently, only results are returned when the primary nodetype matches, thus, when the primary node type is 'hippo:document'.

There should be added a method to find also all nodes (beans) that are a subtype of hippo:document.

Only limitation is, that you cannot search for multiple subtype searches in one go. If you want to search like 'give me all nodes that inherit from hippo:document' you cannot at the same time say, 'or all documents that inherit from hippo:facetselect'