Bug 9216: make columns.def file translatable

The SQL column headers is stored into the columns.def file.
This file is not managed by the translation script.

This patch makes possible the headers translation.
Note: The translation xml tags were added to avoid all lines being put
on a single line.

Test plan:
1/ update your po file
cd misc/translate;
perl translate -f columns update LANG # Replace by another language here
2/ translate header columns (search "columns.def" in your po file).
3/ install the translated columns.def
perl translate -f columns install LANG # Replace by another language here
4/ go on the report module > create a new report > next > next
5/ change the language
on the 3rd step, you should see the column header translated.

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Work as described, no koha-qa errors

[on es-ES about a third of the strings translated!! :-) ]

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Works as described and fixes a long standing translation
problem.
Passes all tests and QA script.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Bug 9216: (follow-up) Make description in columns.def more specific

Changed "Category" to "Patron category" to ease correct
translation.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>