Allow custom value to table.sortable and manage negative values

[Deamon]

Using this change, man can have a specific value which will be used instead of the shown text. Usefull when showing numbers using "fr" locale and use the sort with the "us" locale.

and the second commit allow to manage correctly negatives numbers.

[Deamon]

This is a proposal. The solution is actually working but there might be a better solution to do it! I'm open to any suggestion and improvements!