POC: components for ERT

Use this to not announce ecl_well as a dependency across all projects since symbols only end up in a unit test of opm-core.

@bska POC of what we discussed yesterday. this way the find rule can be synced across projects just fine.
> `list(FIND)` is smart enough to consider an empty list as never holding what we search for and will return `-1`.

Okay, cool.  Thanks a lot for the information.