Got multi install working.

This is quite a bit chunk. Sorry for not splitting it up more nicely.
- multi install works
- on removing a package which other packages depend uppon a message is
displayed and action canceled
- multi update should work also
- renamed onPackageSimpleMessage to onBackendSimpleMessage to reuse it
in packagesModel
- removed quite a lot of duplicated code in packageModel.js
- replaced enyo.error with console.error and cleaned up exception
logging to really work.