Merge pull request #142 from Setono/fix-credentials-validator

Verify api keys with the ping-then-payments probe in the credentials validator

Freshen the README for the 2.0 alpha

- The install command names the constraint that will actually resolve once the
  first 2.0 pre-release is tagged (^2.0@alpha) instead of a non-existent RC
- The Agreement id row now matches the clarified form help text: empty means
  the account's default Payment Window agreement
- The troubleshooting entries no longer point at QUICKPAY_* env vars - in 2.x
  those only feed the test application fixtures; store configuration lives in
  the payment method's gateway form - and the order_id items are reworded
- Drop the duplicated Symfony lock doc link in the Callbacks section

Add mobile number to details

Merge pull request #40 from Setono/upgrade-test-application

Upgrade test application

Support SF6

Remove conflict with proxy-manager, but add it as a dev dep instead b…

…ecause we only need it because there was a bug in 2.13

Remove phpunit config artifact

Merge pull request #35 from Setono/psalm

Added newer code quality tools and fixed psalm errors

Merge pull request #24 from vvasiloi/fix-unit-price

Use full discounted item price which takes into account promotions.

Merge pull request #23 from Setono/disable-capturing

New config option to disable capturing