Talos: merge resources from multiple env-dirs

[tpluscode]

Consider a structure like below, which will initialise a /person/john resource

.
├── resources/
│   └── person/
│       └── john.ttl
└── resources/
    └── person.prod/
        └── john.ttl

When called as talos put resources resources.prod, currently the last will win and ./resources/person/john.ttl will be ignored.

The default behaviour should change so that the both john.ttl should be merged into a single dataset. An optional prefix parameter would allow one to override the other, for example:

prefix talos: <baseResource:replace>