Correct identifier writing.

The attribute for identifiers is "id". This has been corrected in GCTAModelBackground. Further, writing of the attribute has been added to GModelSky. Attributes are also only written if the identifier string is not empty.
For testing, remove -Wno-portability option
Add GChatter to Python typemaps and add specific chatter method for setting of levels from Python.
Put back -Wno-portability option.

An issue has been raied (#1098) to track solving the problem.
Update after chatter change.
Correct precedence of GAMMALIB_CALDB over CALDB (Bug #1094)

GAMMALIB_CALDB should take precedence over CALDB, yet so far the opposite was true. This has now been corrected for.
The GAMMALIB_CALDB environment variable takes precedence over the CALDB environment variable.

This was the initial intention, but the code did the opposite.
Reformat code.
Add vo module and GVOClient class to Python interface.

The vo module and GVOClient class were missing in the Python interface. They have been added now.
Updated code.
Put the test suite test case before the individual test cases that are done within a test suite.

GTestSuite::run starts with creating a test case that collects the total time spent in a test and that also collects any failures of the individual test cases. Before, this test case was appended AFTER running the individual test cases, which led to an XML file out of order. Now the general test case is appended BEFORE running the test cases.
Track results of Python unit tests (#1119)

The results of the Python unit test were not correctly tracked due to some subtle problems related to the way how C++ code is called through the Python interface. A kluge has been found and added to GTestSuite.i to retrieve the Python test results and to propagate them to the C++ test suite, so now Python test results are also written into the XML file, and the Python tests signal failure in case that something goes wrong.
Implement still simplified GCaldb::filename method.

The GCaldb::filename method returns an absolute IRF filename based on a set of selection criteria. The selection criteria are still very simple, and a more sophisticated should be implemented in the futur. For the time being, the method does the job.
Add dummy IRF.
Remove old Prod1 performance tables from repository.
Remove old IRF files
Add new Prod1 calibration files (for testing purposes)
Update calibration index file after updating IRF test files.
Install caldb instrument response functions
Adapt unit test to new PSFs and add GCTAPsfKing class tests.