Enabled shutdown functionality of DcmSCPPool.

Finished implementation of DcmSCPPool::stopAfterCurrentAssociations().
Some basic tests have been run to ensure this method works as expected.
Fixed wrong tag in CodingSchemeIdentificationSequence.

Fixed wrong tag being used in CodingSchemeIdentificationSequence (0008,0110).
Instead of Responsible Organization (0010,2299) it should be Coding Scheme
Responsible Organization (0008,0116). This inconsistency was introduced back
in the year 2003 with CP-324. This commit also changes the name of the
corresponding get/set methods in class DSRCodingSchemeIdentificationList.