Complete Refactor of ExAdmin

We've had issue #166 open for a long time. @dsnider and I have been working on some ideas that we think will make ExAdmin much more extensible, and fit better with the "Phoenix and Elixir" way. I have started working on prototyping of a complete overhaul of the ExAdmin architecture.

Justification

ExAdmin was developed for my first Phoenix Application. The approach I took, although functional, does not align very well with the Phoenix way. Furthermore, I feel that we can do better without the heavy use of DSLs. Finally, I've never been happy with the theme support implementation.

Design Goals

• break the package apart into a series of composable components
• make it simple to customize every part of the package
• remove the dependency on Ecto Schema. .i.e json objects, etc.
• easy to drop in new themes
• easy to update with extensive customization
• still works out of the box, without the need to configure anything
• intelligent defaults
• optimize the architecture to support large data (no association drop-downs with thousands of entries)
• support multiple themes/layouts in a single application (front facing layout and a back office "admin" interface)

Ideas being kicked around

• Use JS data tables for the index page
  • live search/filtering
• Revamped sidebar filter
  • live updates
  • more inline with product filters on an eCommerce site
• Resource modules based on behaviours instead of config
• Perhaps more of a plug architecture (not sure what that looks like yet
• Remove the html DSL and replace it with Slim templates
  • Could use eex, but I much prefer indentation based templates
  • Could use both if we get pushback on Slim
• Customization with generators that create templates of templates
  • prototyping this now
  • avoid the sensitivity of direct generators when updating ExAdmin
  • might making theming much easier
• componentize each concern (views/templates, controllers, schema)
• buffer the dependency on Ecto to support other approaches to describe and reflect the schema of resources

This will be a break point release. No backwards compatibility.

I welcome your ideas and feedback. Steve