added .gitignore
made package stores optional

i.e. fixed error when `instance_pkgstores` was missing from
configuration; a package store is not always necessary/desired
made store structure optional

this is the logical conclusion from the previous commit
(467942d84db74a277c8ce1bfda8d84f4022d9eec)
fixed use of quotes for consistency
Merge pull request #3 from FND/nopkgstore

made package stores optional