Add more comfortable methods to KnowledgeManager

[jiracekz]

In order to get a knowledge from the knowledge manager, one has to build a KnowledgePath and call get(Collection). It would be useful to also have a method get(Collection) and get(String) which would read knowledge based on knowledge path expressed as a string.

Alternatively, a method that creates a KnowledgePath based on String could be introduced.

[iliasger]

We need to make the existing API for it public and possibly enhance it