Merge dev into feature/436-include-layouts
- Include layouts in package.xml and destructiveChanges.xml generation
- Remove unpackaged metadata uninstall from uninstallCumulus, only
  uninstall packaged metadata
Merge branch 'feature/436-include-layouts' of github.com:SalesforceFoundation/Cumulus into feature/436-include-layouts
Merge pull request #439 from SalesforceFoundation/feature/436-include-layouts

Include layouts
Merge dev into feature/416-depend-on-beta-pkg