Don't show containers in deployment summary.

* Filter out container only changes in the `_addMachines` case of `_getChanges`
* Added `_noMajorChanges`, which determines if there are any so-called "major"
  changes in a given change set.
* Updated the handlebars template to show the summary only for "major"
* and to toggle the changelog by default if there are only "minor" changes.
* Updated tests.
Comments from review and test changes.
Merge pull request #443 from jaycee/no-containers-in-deploy-confirm

Don't show containers in deployment summary.

* Filter out container only changes in the `_addMachines` case of
`_getChanges`
* Added `_noMajorChanges`, which determines if there are any so-called "major"
 changes in a given change set.
* Updated the handlebars template to show the summary only for "major"
* and to toggle the changelog by default if there are only "minor" changes.
* Updated tests.