2.0 Milestone discusison

[scaytrase]

This plugin lacks a bunch of refactoring so I think we need some fresh ideas for it. My current thougs are

• Split server configuration and notification logic, possibly re-use other plugins, who provides bitbucket server\cloud configuration
• Allow multiple commits to be notified (Allow multiple Stash Notifiers per Job #61 Allow multiple commits notified per server #90)
• Split notification logic into classic freeconf post-build step and other instances (pipeline dsl step, freeconf build-step, freeconf pre-build flag) cc. @0xorial
• Support cloud notification (Bitbucket cloud support #85)

At the moment I fully satisfied by features provided by Jenkins Blue Ocean and Bitbucket branch source plugin, so I see no extra use-cases for me personally, but I'm glad to make this plugin useful for someone else