Investigate reducing config in site.json without repeating in plugins and pluginsContext

[crphang]

Tell us about your environment

• MarkBind Version:

Master

Current Usage To Add plugins

To add plugins, users have to add two keys to site.json, plugins and pluginsContext as described in the userGuide:

Preferred author experience

As an author, I would only want to type a single key, preferably as follows:

"plugins": {
    "algolia": {
    	"input": "Input for Plugin 1"
    },
    "googleAnalytics": {
    	"data": "Data for Plugin 2"
    },
  }
}

The benefit of this are:

1. Harder to make mistakes
2. Less things to type to achieve what I want

If necessary, we could always get plugin names from plugins.keys() to read from the plugin directory.

[damithc]

This point came up when we added the plugin feature. @acjh pointed out some benefits of keeping them separate. We can reconsider if there is a way to keep all benefits and overcome all the downsides.

[crphang]

Hmm, I see. I changed the title a bit, we could leave this for investigation until we could come up with a potentially better user experience