Update bundle size optimization for Blueprint Icons

[amcclain]

Reviewing a recent bundle treemap on our Toolbox app, it looks like the big Blueprint icons package has returned and is taking up a lot of space again. My bet is that something about the path changed, and the workaround we implemented in #25 a while back needs to be updated.

[amcclain]

@cnrudd if you have a chance to review - we could look together tomorrow as I'd like to cut a dev-utils release with an even bigger fix to FontAwesome icons.

[cnrudd]

Looking now.

[cnrudd]

This has been fixed in this hoist-dev-utils branch:
https://github.com/xh/hoist-dev-utils/tree/bpIcons (see PR)

and can be tested easily in toolbox branch bpIcons.

BP4 brought in a requirement for using a new method for getting the icon name, which I have added into the requireBlueprintIcons.js file and moved the file (as per discussions) into the hoist-dev-utils project to avoid creating a breaking change dependency between hoist-dev-utils and hoist-react.

(See palantir/blueprint#2193 (comment) for more details on the new method)

I have committed some temporary changes to the package.json files in the bpIcons branches of toolbox and hoist-react that load hoist-dev-utils and hoist-react from specific commits in the bpIcons branches. This makes it much easier to run the project for the purpose of testing this change and to do bundle analysis.

Bundle analysis on the build using the bpIcons branch of hoist-dev-utils shows a much smaller BlueprintJS Icons package.