relax SVN archive

Fix for bug #21924 (https://gna.org/bugs/?21924).

This is the failure to output 2D Grace plots for the R20, R20A, R20B, and R1rho0 relaxation
dispersion parameters. A simple test for missing data fixed the problem.

The relaxation dispersion auto-analysis now outputs the R20, R20A, R20B, and R1rho0 parameters.

This includes both text files and 2D Grace plots.

Updated the text for the software verification tests in the test suite.

Shifted the relax library independence developer script into the software verification tests.

The functionality of the devel_scripts/test_library_independence.py script is now within the
Library.test_library_independence software verification test. Therefore the script has been
deleted.

Created a new test category for the relax test suite - the software verification tests.

This is part of the full test suite or can be run by itself using the new --verification-tests
command line option. Such tests are best described by
https://en.wikipedia.org/wiki/Verification_and_validation_%28software%29. These tests will be used
to make sure that the design aims of the relax source code are satisfied. For example that the
relax library is independent from the rest of relax. Or that the package __all__ lists actually
contain all modules and sub-packages (these tests are currently part of the unit tests).

Editing of the relax command line option descriptions.

Removed the automatic axis labelling in the lib.software.grace.write_xy_header() function.

This is the automatic labelling based on the parameter Grace strings and units of the specific
analysis type. This is now preformed by the specific analyses themselves so the automatic code is
not needed or used.

This allows the dependence on the pipe_control.pipes module and the specific analysis API to be
removed making the relax library now 100% independent from the rest of relax.

Shifted many of the pipe_control.structure.geometric functions into the relax library.

All but two functions from the pipe_control.structure.geometric module are independent of the relax
data store. These have been shifted into the new lib.structure.geometric module. This removes most
of the remaining relax dependencies in the relax library.

Shifted the data_store.relax_xml module into the relax library as lib.xml.

This module contains a couple of functions which are used for converting Python objects into an XML
representation and back again. These are used not only by the relax data store, but also a number
of the structural objects in the relax library (which are themselves placed in the relax data
store). This makes the relax library more independent from the rest of relax.

Huge clean up of all unused imports in relax.

These were found using the find_unused_imports.py development script. A number of these changes
significantly decrease the possibilities of circular imports appearing in the future. And this also
makes the relax library more independent from the rest of relax.