PHP-232 - Implement Jenins CI using declarative pipeline syntax

- Per-commit, scheduling, and adhoc testing
  - Adhoc testing adds the ability to run one or all server versions
- Adds parameters for adhoc building, testing, and deployment
  - Uses HTML descriptions for external users
- Descriptive builds for Jenkins UI
- Log rotation is used to minimize server storage
- Timeouts are used for entire pipeline and per particular stage
- Artifacts are archived in Jenkins for per-commit builds
  - Artifacts force into PHP version specific directories; avoids overwrite
- Error logic to archive logs for evaluating issues
- Allow AppVeyor to ignore Jenkins pipeline changes
- Add Slack notifications for start and end of runs
  - Per-Commit and scheduled runs only
- Adding the ability to set server version and verbosity (integration)

Note: All Server versions for scheduled/adhoc are available. This
required a workaround due to the following Jenkins issue,
https://issues.jenkins-ci.org/browse/JENKINS-37984.

Author: Michael Fero