Extend data sources

[irm-codebase]

Is your feature request related to a problem? Please describe.
GADM has seen a certain degree of instability in its data (i.e., downloads break down inconsistently).
We should extend our sources to more stable ones.

Describe the solution you'd like
Add newer datasources that are:

1. Versioned
2. Stable (good APIs, stable access, versioned)

Candidates:

• World Bank boundaries
• geoBoundaries

[irm-codebase]

#59