Added maven pom.xml; exception classes & exception handling, rados shutdown method

- added maven pom.xml with needed dependencies (if wanted build.xml for ant can be removed)
		run 'mvn clean test' for testing; 'mvn clean package' for creating a jar
- changed rados to handle all exceptions in one method
- changed to throw more specific exceptions depending on the returned error code by librados
- if no specified exception matches a list of all error codes with name + msg is defined which will be returned for more information
- removed unneccessary memory allocation in Rados#poolList()
- added shutdown method to rados to be able to close the connection explicitly (not only by gargabe collection)
- tiedied up tests to create and destroy connection/iocontext only once in @beforeclass and @afterclass and not for every test
- removed unused imports

Questions:
- what is the Library class in rados and rbd good for? the methods implemented in there are afaics nowhere used?
- i did the changes only to the rados binding; if you want to you can either do the same for the rbd binding or let me know and I can do it as well...