Splitting up Grunt watch into separate tasks to improve performance

[theorise]

I am using Pattern Lab Node v1.3.0 on Mac, using the grunt configuration.

Expected Behavior

The grunt watch task rebuilds:

• Patterns when updating .mustache files
• CSS when updating .css files
• JS when updating .js files

Actual Behavior

The grunt watch task rebuilds everything when running the watch task. This makes developing inside Pattern Lab a painful process once you have a large pattern repository.

Steps to Reproduce

Run grunt serve in a repository with a lot of patterns, update a style, see that you have to wait for the patterns to rebuilt despite having no changes.

[bmuenzenmeyer]

closing as superseded by edition-node-grunt and lack of response on #289