relax SVN archive

Updated the data model chapter of the user manual to cover the handling of protons.

This change includes the modification of the PDB reading screenshot to demonstrate the reading of a
specific model and the naming of the molecule.

All of the GUI strings and text are now formatted with a small sans serif font in the user manual.

This is because in the GUI, a sans serif font is almost always used be default.

Fix for bug #20177 (https://gna.org/bugs/?20177).

This was simply a lower precision OS/Python/numpy combination causing a test suite failure - there
are no practical effects and only the precision of the system/GUI test has been lowered.

Another bug fix for the sequence GUI editor window.

This bug was being triggered by the User_functions.test_structure_pdb_read() GUI test which now
passes.

Small fix for the User_functions.test_structure_pdb_read() GUI test.

Modified the User_functions.test_structure_pdb_read() GUI test to catch another bug.

This is a bug recently introduced with the fixes to the other sequence editor GUI window problems.

Fix for bug #20184 (https://gna.org/bugs/?20184).

The behaviour of the gui.string_conv.gui_to_int() and related functions has changed in the last few
months and the Sequence_window() GUI element has not changed to match. This has been fixed and the
User_functions.test_structure_pdb_read() GUI test now passes.

Fixes for the User_functions.test_structure_pdb_read() GUI test.

Created the User_functions.test_structure_pdb_read GUI test for checking the sequence editor window.

This new user function GUI testing class is to be used for testing out the special GUI elements not
invoked within the unit testing. The test_structure_pdb_read() test specifically shows a number of
failures of the sequence editor window.

Modified the operation of the sequence GUI element to have access to the sequence editor window.

This is to allow this GUI element to be blasted within the test suite.