A table widget

**- Do you want to request a *feature* or report a *bug*?**
Request a feature

**- What is the current behavior?**
Managing basic lists (such as a price table) is often a regular part of managing content for a site or web app
As it stands now, there is no way to define a list of items (texts) that is easy to read AND edit, due to the way the interface is designed (input field after input field after input field is not the same as a compact list, or table)

**- What is the expected behavior?**
A simple table structure to add content in. I will use [Webhook](http://www.webhook.com/) as an example since it's a fantastic CMS with a fairly nice and simple solution to implement tables.

[Here is how you enter the data, based on the defined data structure (columns)](https://dl.dropboxusercontent.com/s/xzgmcqfq0813840/shot_171222_141005.png)

**- Please mention your CMS, node.js, and operating system version.**
Netlify CMS version 0.4.6
WIndows 10 64biy
node.js v8.4.0