Phoenix 1.7

[andyl]

Now that we have a RC for Phoenix 1.7, along with Phoenix LiveEditable 0.18 with JS actions, slots and attributes, I'm going to try to get this repo into MVP working condition.

Phoenix LiveEditable will continue to be structured to support multiple CSS frameworks, but now the Tailwind support looks really good, and my core efforts will focus on Tailwind.

I will experiment with PhxLiveStorybook to see if that might be a good way for people to demo Phoenix LiveEditable components. Also I will experiment to see if there can be a straightforward way for people to tweak the built-in styling of the LiveEditable components.