• Uses the config proposed in NPM scenario support #26, with an npm and bower key under each scenario, then the dependencies and devDependencies (and resolutions, for bower) under that. The old configuration format is still supported, but only for bower dependencies.
• Supports npm dependencies, at least some way: Backs up node_modules and package.json before any commands are run, modifies package.json based on the scenario, runs npm install and npm prune, runs the command, and to cleanup, restores the package.json and node_modules folder and runs npm install and npm prune.
• Unifies the code path for ember try and ember try:testall
• New output for the results of running a scenario that shows the dependencies that were changed, what was specified in the config and the actual version that was used.
  
• Many more tests
• Upgrade ember-cli

Limitation: Currently packages can be removed between scenarios (thanks to npm prune) but packages in package.json cannot be removed. This needs further thought and perhaps our own configuration syntax. This is the same as the current support for bower.

Further things to do:

• Need checks against trying to vary ember-try between scenarios.
• Use semver comparison to determine status of dependencies in output table (right now strict comparison)
• Maybe warn if trying to vary ember-cli between scenarios.
• Find out if this works on Windows.

Important Note: When specifying packages for npm in scenarios, remember to put them in the same "bucket" as in package.json -- devDependencies go under devDependencies, and so forth.