Emit a CMake configure-time warning if the avogadrodata directory is not there
Emit a CMake configure-time warning if the avogadrodata directory is not there

It should be a sibling to avogadrolibs. This warning will help pinpoint dashboard
machines that do not have things checked out / laid out properly as well as
help individual devs who are checking out avogadrolibs independently (not as
part of a superbuild arrangement...)

Change-Id: Ic5523dc24af79f0a3cd71ab33b0d73218f2baa4e

OpenChemistry/avogadrolibs,wadejong/avogadrolibs,cjh1/mongochemweb-avogadrolibs,ghutchis/avogadrolibs,wadejong/avogadrolibs,ghutchis/avogadrolibs,OpenChemistry/avogadrolibs,ghutchis/avogadrolibs,OpenChemistry/avogadrolibs,OpenChemistry/avogadrolibs,wadejong/avogadrolibs,ghutchis/avogadrolibs,cjh1/mongochemweb-avogadrolibs,cjh1/mongochemweb-avogadrolibs,OpenChemistry/avogadrolibs,ghutchis/avogadrolibs,cjh1/mongochemweb-avogadrolibs,wadejong/avogadrolibs