Make a default `all` range variable

[aspiwack]

Right now, I have to write all in any logic. Instead, I should list of the locations at the top of the file (for scope checking see #11 , and for location capacity see #12 ), and have, by default, a range variable all with all these locations.

Open question: does this allow for several location sections? Maybe we should have an all variable per location section? I don't know yet.