List item types and controls

[jscharf]

This project uses semver, please check the scope of this pr:

• [ ] #none# - documentation fixes and/or test additions
• [ ] #patch# - backwards-compatible bug fix
• [x] #minor# - adding functionality in a backwards-compatible manner
• [ ] #major# - incompatible API change

You can now specify itemTypeKey, componentKeyNames, and componentKeyNamesForTypes in addition to changing controls from an array of components to a hash of components, in order to produce an object browser that can take advantage of this new functionality. It can conditionally show certain controls based on the type of the list item. If multiple list items are selected, it will only show the controls that are applicable to all of the selected items.

CHANGELOG

• Added ability for object browser to render list list items with different types
• Added ability for action bar to show certain controls based on list item type

[dafortin]

LGTM. Please check comments before merging.

[jscharf]

I cancelled the previous build because I pushed another commit to remove the unnecessary checks from a computed property. Now I am just waiting for the next build to finish before I merge.