Add Spree::Admin::RootController for redirecting purposes.

Currently, is really difficult to redirect to a different tab when the
user has logged in if said users cannot at least :admin, :index
`Spree::Order`s.

This commit adds a controller that handles `/admin` route so anyone can
easily redirect to another page (or implement any other logic).
Remove 'disabled' from inputs in payments

With the Aug 27 commit, a601035bd199a49f7f74ccf04ed0d889ca895f3e, the inputs under `.payment-method` are being disabled on line 15 but never correctly undisabled. This fixes that issue. Looks like it is affecting most branches.
fixes #5467
fix handling of credit cards expiring in current month
fixes #5468
Add Heroku deploy button.
Update app.json
Add buildpack url.
Remove deploy to heroku button. Fixes #5401
Add issuestats badges.
Add Spree instrumentation

Add instrumentation to some checkout methods

Fixes #4802
Make best-promotion query more deterministic

Mostly for the benefit of the specs under MySQL.

This query was generating some sporadic spec failures for me when using MySQL as the database. This is because MySQL does not store fractional seconds so the "created_at" was sometimes the same value for two adjustments when running specs. And when created_at is identical the query below would actually pick the earlier adjustment instead of the more recent one.  Adding "id" as a fallback ordering fixes this problem and makes the behavior more deterministic.

The issue is reproduceable in postgres as well by using Timecop.

Fixes #4943
fix spelling for interim in image model--skip-ci
fixes #5469
Fix running just rake for specs.
Fix rerunning sample specs without new dummy app.
Refactor Promotion.applied scope to query faster

* Before the scope did two joins. Joining the join table and than the
  orders table. As joining the join table is sufficient to define the
  result set removing one layer of joins significantly speeds up the
  operation on large order tables.

Fixes #5453
Assign store id to each order.
Associate new exchange orders with the same store as the original order

Replaces #110.

Fixes #5440
Remove check thats no longer necessary.
Bump version.
Revert "Add Spree instrumentation"

This reverts commit 48669ed26f9ae7e1f07a31f19fbce794ce44ef9c.
Bump version.