Initial commit for server-based features.
Additional error checking. Feature ringdown = features API then featurelist.dev.js then featurelist.js
Using wx.formbuilderAdvanced as default advanced option if it exists (overridden by Feature API).

Merge branch 'formbuilder' of github.com:WeeverApps/weever-plugin-common into formbuilder

Conflicts:
	js/models/subtab.formbuilder.js