Allow category descriptions to be updated

[moi90]

It was proposed to use the PATCH verb to modify the description of a category (by JO, Julie and Bea):

PATCH /taxon[/central?]/{taxon_id}]

{source_desc: "..."}

This would be helpful to update the descriptions of categories to add tag-related data.

[grololo06]

Hello, thanks.
We "just" have to define the security around this function, unfortunately taxa have no "owner", they are created on-demand but then virtually belong to EcoTaxoServer admins.

[moi90]

Yes, that is a problem... In fact, the creator is stored. But I would also like to edit categories created by others. And it would also be bad if the EcoTaxoServer admins had to edit hundreds of categories by hand...