Remove "final_demand" type from non-FD nodes

Although many of these nodes contain "final_demand" in their name, and
are in fact final demand nodes in ETEngine, in Atlas+Refinery, the type
is used to indicate that the node document MUST have a query and
associated value in a CSV file. Many of these nodes do not have -- and
are not expected to have -- such a value.

This fixes the failing (actually, skipped) validations on these nodes.
Ref #283.
Validate share files

* Asserts that the file contains :key and :share headers.
* Asserts that the shares sum to 1.0 (within a 1e-12 margin of error).

Ref #283