Added coil label section to acquisitionSystemInformation

This commit contains:

1. coilLabel section of XML header
2. C++ library support for this new section
3. Bug fix regarded referencedSOPInstanceUID in XML file
4. Updated example XML documents
5. Added ismrmrd_test_xml program (only for development purposes)
6. Fixed some warnings from C applications
7. Updated XML header version to 2
8. Updated library version to 1.2.0
9. Updated SHA1 hash for new schema. 

Not done:
1. Matlab XML serializer/deserializer to accommodate new schema elements