Add new/delete for most/all resources #58

Currently, some resources are global and always open. With this change, we could e.g. introduce the ability to create and delete new KV stores, so that unrelated keys don't have to be stored a single KV.

In order to help with migration from v0.2 to vNEXT, we should have some global resources pre-opened (e.g. KV store with id=0), so that existing plugins could be recompiled without any code changes.

This should be advertised behind a settings/feature flag, so that we can eventually get rid of them.