Improve Affiliate Linking, Add Affiliate Tracking, Add Commission Rules

1. Advertiser (Store Admin) creates an affiliate.
2. Advertiser defines the commission rules for affiliate. Currently, we have set 2 rules for commission:
   a. If consumer signs up to Advertiser's site. - Certain amount.
   b. If consumer purchases from Advertiser's site - Certain percentage of order total.
3. 'Affiliate Link' is generated which can be used by Publisher.
4. Publisher uses the affiliate link on his/her own site/blog.
5. Consumer visits Publisher's site and follows the Affiliate Link.
6. Consumer signs up to Advertiser's or purchases the product/s from Advertiser's site.
7. All of the affiliated traffic is to be tracked weekly, bi-weekly or monthly by user cookies to pay against apt affiliate.

v3.1: Merge pull request #3 from vinsol-spree-contrib/update-ux

fix UI and UX

v3.0: Merge pull request #2 from vinsol-spree-contrib/UI-fixes

fix UI and UX

v2.3: Merge branch 'master' into 2-3-stable

Conflicts:
	README.md