relax SVN archive

The table contents are now all converted to strings in lib.text.table.format_table().

This uses the _convert_to_string() private function.

Created a new unit test of lib.text.table.format_table() to check for non-string type data.

Slight changes to one of the lib.text.table.format_table() unit tests.

Fix for calculating column widths when multi-column cells are present in lib.text.table.format_table().

Spacing between heading rows is now functional in lib.text.table.format_table().

Implemented multi-column support in lib.text.table.format_table().

Created a unit test for the lib.text.table.format_table() function to test multiple column support.

Support for content spanning multiple cells is yet to be implemented.

Fix for bug 20603 (https://gna.org/bugs/?20603), the relaxation data right click menu failure.

The problem was that there was that the last menu item specified had no contents. This item has
been removed.

Modified the Mf.test_mf_auto_analysis GUI test to catch bug #20603 (https://gna.org/bugs/?20603).

Created the lib.text.table.MULTI_COL constant for defining cells spanning multiple columns.

This is not used yet.