MiscUtil: migrate to exception logging
- Migrates error logging to new exception-based technique. (addresses #580)
- Creates class InvenioMiscUtilError and adds the methodsinit() and str().
- Deletes functions 'register_errors()', 'get_msg_associated_to_code()', 'get_msgs_for_code_list()', 'log()'.
- Deletes var CFG_MISCUTIL_ERROR_MESSAGES.
- Deletes tests in 'errorlib_tests.py' that use this variable and these removed functions.
- All Invenio modules are now migrated to exception logging. (closes #580)