Refactor to redux, query components, & the wordpress-rest-api module

[ryelle]

stream of consciousness PR, mostly for personal notes

Adds redux + query components in a submodule; perhaps eventually to be released as an npm module – or two? trying to separate them out was harder than it seemed, but a lot has changed while working to this point. trying again in the future is possible. Might also disregard the "ducks" approach if so, and bundle instead with each query-component?

Other updates:

• Injects the nav menu as an object into the page, rather than calling the API to load it.
• Removes gulp
• es2015 refactor
• Switches to react-router (from page), which introduces new routing.
• Permalinks need to change slightly -- /page/X is now /p/X, date archives are prefixed with date, pages prefixed with page.

Somewhere along the lines I've introduced a javascript error Uncaught TypeError: Cannot read property 'replaceChild' of null — but everything appears to work anyway? Thinking it's related to the query components. (will handle in future commits)