store handlers for viewing, creating, and editing coupons

[cdepillabout]

I'll do this.

[cdepillabout]

This includes the following 6 handlers:

• GET my store coupons
  - show list of all coupons
  - GET http://$domain/store/coupon
  - storeUser_store_coupon.pug
• GET my store coupon detail
  - show individual coupon
  - GET http://$domain/store/coupon/${coupon_id}
  - storeUser_store_coupon_id.pug
  - Same as coupon detail page for end-user except that this page has some links for store user.
• GET my coupon create page
  - page for creating a new coupon for a store
  - GET http://$domain/store/coupon/create
  - what is the pug file???
  * pug file for "GET my coupon create page" api #76
  * let's reuse the storeUser_store_coupon_id_edit.pug with making
  the word "編集" changeable by template variable. (I guess it's
  better to use English word such as "Edit"/"Create" for the
  variable.)
• POST my new coupon
  - POST a new coupon
  - POST http://$domain/store/coupon
  - on error shows pug file from "GET my coupon create page" (storeUser_store_coupon_id_edit.pug)
  - redirects to "GET my store coupons" on success
• GET my coupon edit page
  - edit an existing coupon
  - GET http://$domain/store/coupon/${coupon_id}/edit
  - storeUser_store_coupon_id_edit.pug
• PUT Edit my coupon
  - edit an existing coupon
  - PUT http://$domain/store/coupon/${coupon_id}/edit
  - on error show the pug file for "GET my coupon edit page"
  - redirect to GET my store coupons on success

[cdepillabout]

GET my coupon create page and POST my new coupon have been implemented in #82.