this allows tag values to contain spaces, which is up to your own micropub server to handle appropriately.

closes #95 and replaces #96

closes #67

allows backdating and future-dating posts

fixes #9

* looks for a media endpoint in the micropub config
* if media endpoint is available, both the note interface and the editor will upload files to it instead of posting the photo directly
* the note interface autosaves in-progress notes in localstorage

* it sometimes confuses web servers to have a folder named "editor" while also serving routes with the same name
* dropped appcache stuff since it wasn't working super well
* add nginx config to the readme