Improving grunt watch task performance

[theorise]

Addresses #287

Summary of changes:

• Added .svg extension to image copy task.
• Split watch task into patterns, styles and js groups.
• Split browserSync reload into two tasks, css and js.

This has highlighted a problem with the browserSync reload task #288. I am not sure if I have messed something up here, or if this problem already exists,

[bmuenzenmeyer]

Checking this out now

[bmuenzenmeyer]

• With these changes, the grunt tasks default and serve still have references to the old copy and watch tasks.

I changed

  grunt.registerTask('default', ['patternlab', 'copy:main', 'copy:styleguide']);

to

  grunt.registerTask('default', ['patternlab', 'copy:all']);

and

  grunt.registerTask('serve', ['patternlab', 'copy:main', 'copy:styleguide', 'browserSync', 'watch:all']);

to

grunt.registerTask('serve', ['patternlab', 'copy:all', 'browserSync', 'watch:patterns', 'watch:styles', 'watch:js']);

in an attempt to fix this.

• Running grunt serve does reload styleguide when a pattern changes
• Running grunt serve does not, however, pickup changes made to ./source/css/style.css or ./source/js/init.js

@theorise please review - perhaps I am doing something wrong? I've pushed my attempted fix to a branch of the same name as this PR.
https://github.com/pattern-lab/patternlab-node/tree/theorise-grunt-performance

[bmuenzenmeyer]

closed due to lack of response and inappropriateness for this repo. moved a link to it to pattern-lab/edition-node-grunt#3