Allow to synchronise all articles + category matching

The current shared database functionality is geared towards wholesale retailers. When subscribing to a farmer's article list, foodcoops need to import new articles every time. This change allows one to specify how to do synchronisation for a supplier: (1) Import all articles, (2) Import all articles but make them not available yet, and (3) Manually import articles (current functionality). In the first two options, the full article list from the suppliers is always included in foodsoft (this option is not allowed with >200 articles).

Also categories from shared articles are copied when there is a matching category, either in name or in description (which is renamed to "import names" in the user-interface - it wasn't really used).

One step closer to automatic synchronisation (see also foodcoops#187).

- [ ] Reword selectbox in edit supplier