Restructure filesystem to better align concerns and support upgrades

[bmuenzenmeyer]

Addresses #133

Summary of changes:

• moved builder/*.js files and fixed all references
• move source/_patternlab-files/partials to core/templates
• move source/_patternlab-files/pattern-header-footer to core/source/_meta
• move source/eveythingelseish to core/source ?????
• "Open in new window" should be a page with no PL JS #265 moving off this PR
• meta patterns missing? #169
• testing
• add support for {{ cacheBuster }}
• as of writing, passing unit tests and building frontend

[geoffp]

YES

[bmuenzenmeyer]

I was initially going to put the shipped patterns into core/source and then build a mechanism to move them over into config.source.* path, but I don't really see a big benefit aside from having a clean copy if a user wanted it. Need to think about it more. Thinking through to the eventual inclusion of starter kits, seems easier to deviate from this PHP pattern