Add Symfony Deprecation Contracts package

- Created CHANGELOG.md to maintain version history.
- Added README.md with usage instructions for the trigger_deprecation() function.
- Initialized composer.json for the Symfony Deprecation Contracts library, specifying dependencies and autoloading.

modules/pshowsso/deps/stevenmaguire/oauth2-keycloak/CHANGELOG.md

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+# Changelog
+All Notable changes to `oauth2-keycloak` will be documented in this file
+
+## 2.1.0 - 2018-03-12
+
+### Added
+- Introduce `getLogoutUrl` method on provider to build and return and authorized logout url - thanks @FlxPeters
+
+### Deprecated
+- Nothing
+
+### Fixed
+- Nothing
+
+### Removed
+- Nothing
+
+### Security
+- Nothing
+
+## 2.0.0 - 2017-01-25
+
+### Added
+- PHP 7.1 Support
+
+### Deprecated
+- Nothing
+
+### Fixed
+- Nothing
+
+### Removed
+- PHP 5.5 Support
+
+### Security
+- Nothing
+
+## 1.0.0 - 2017-01-25
+
+Bump for base package parity
+
+## 0.2.0 - 2016-12-07
+
+### Added
+- JSON Web Token decryption support
+
+### Deprecated
+- Nothing
+
+### Fixed
+- Nothing
+
+### Removed
+- Nothing
+
+### Security
+- Nothing
+
+## 0.1.0 - 2015-08-31
+
+### Added
+- Initial release!
+
+### Deprecated
+- Nothing
+
+### Fixed
+- Nothing
+
+### Removed
+- Nothing
+
+### Security
+- Nothing