Create education-specific data package

[trey-stafford]

An education-focused QGreenland package would include only layers useful for curriculum materials developed around QGreenland, and would exclude some science layers that may be confusing to beginners (e.g., error estimate rasters for modeled variables).

Alyse has developed a document with thoughts about which layers would be important to keep/remove for such a package here

[twilamoon-science]

See note about using map themes on issue #657

[trey-stafford]

Relies on #714