Regression notification implemented.

[prashantkalkar]

Notification generated for following cases:

• If number of failed tests increased. (Even when previous build was red).
• If the failed tests are different than previous build (Even when the number of failed tests are same as last build).

Will not notify for

• For failure that are same as previous build.

In short, will notify if the current build is worst than the previous build.

[samrocketman]

@prashant-ee can you rebase instead of merge?

[samrocketman]

This has been thoroughly tested with Slack and Mattermost using https://github.com/samrocketman/jenkins-bootstrap-slack.

• ✅ The plugin smoothly upgrades without breaking existing configurations.
• ✅ The code integrates well with existing configurations.
• ✅ You have included tests!

Thanks for your contribution. This will be merged pending a CI validation of your rebased commit.

[prashantkalkar]

Thanks for accepting the changes​. Happy to contribute.