Refactor data import code.

Add a class iris.elt.loader.Loader which provides two methods:
* sync_entity: create/update/delete entities
* sync_nnr: add/remove many to many relationship

Import script only need to rely on these two simple APIs in
order to hide complex syncing logic but only focus on business
logic.

Also add a helper class UserCache. It caches all user strings
in scm text files and merge user's first name, last name and
email. It also builds a index to retreive the user by string
written in scm text files.

Change-Id: I9cfdf12bd137b497d6c0c5eb38b8b8f124937eb2
Depends pyquery from 1.2.4 to 1.2.8

IRIS repo provides the latest version of this package.

Fixes: #2021
Change-Id: Ie7c39045871f7e8c0e67f514bc7dcf70b1be1dbd
Update README

Add a section for new commers about how to contribute to this
project.

Also Remove emails in this file, since it's public and I will
push code to github, so we'd better to remove this internal
emails at first.

Change-Id: Iafe7eb0108738d335444d0c763ed165430a542ad
Update AUTHORS file.

Add all developer's names into AUTHORS file.

Change-Id: I8525e799749d0a85a1bf11eadb3a23131c5c7003