Follow Makefile 'include' directives

[jamesaoverton]

ODK always uses this, so it would be good to support them.

[matentzn]

This is very important for our ontology and linkml projects - the extended (included) Makefile is now a pervasive pattern.

I am assuming that when I run a goal "x" that is in the Makefile (which includes project.Makefile) that, if the x is overwritten in project.Makefile, DROID is, even now, running the x as specified in the project.Makefile (analogous to what a make invocation on the command line would do)?