fixed issue in ResolveFeatureType operation when repo is empty
Modified import operations to avoid changes in feature types and prevent creating trees with mixed feature types

Importing different feature types is still allowed, but it has to be explicitly indicated
Merge remote-tracking branch 'origin/pr/703'

Conflicts:
	src/geotools/src/test/java/org/geogit/geotools/plumbing/ImportOpTest.java