Remove readWorsheet.disjoint from Zonator

Not really part of the core functionality.
Document read-output-rasters
Change package options from list to env
Getter and setter for Z tutorial location
Move open.dir implementation to zproject-methods
Remove open.dir from utilities
Add zonation-tutorial as a submodule
Start working on tests
Merge branch 'master' of https://github.com/jlehtoma/zonator