Added ART API for stored model

[tmushayahama]

@lpalbou and I worked on making temporary stored model api until diff as per this comment #364

This is to show sample code. This is a working art api to get the stored model

The approach of separate API doesn't cause any side effect as it is readonly and easy to extend without hustles. It uses the same concept as searchAPI with jetty. Take a look how it is decoupled with m3Batch

to get the store endpoint is

from minerva http://localhost:6800/search/stored?id=gomodel:5fdc2fda00000000
from barista http://localhost:3400/search/stored?id=gomodel:5fdc2fda00000000

reason for search endpoint is temporary testing as barista only allows search proxy

tagging @lpalbou @balhoff @kltm

[tmushayahama]

I have added the initial tests and ready for review and merge.

tagging @balhoff @kltm @lpalbou

[tmushayahama]

As discussed, I have fixed the equal and not using the JsonModel equal function @balhoff @lpalbou . Thank you all for going over this. The call really helped.