Adds the maximum table size to export option (Feature request 1515)

Added a textbox to the custom export options, in the loop where the
Exporting is done, I added a query which checks the current table's size.
If this size is greater than the limit specified we don't export the current
table.

Signed-off-by: Aditya Sastry <ganeshaditya1@gmail.com>
Fix merge conflict

Signed-off-by: Marc Delisle <marc@infomarc.info>
Signed-off-by: Marc Delisle <marc@infomarc.info>

- localize the size suffix
- improve XHTML
- the label needs an id
- add a todo
ChangeLog entry

Signed-off-by: Marc Delisle <marc@infomarc.info>
Update po files
Translated using Weblate (Spanish)

Currently translated at 100.0% (2760 of 2760)