Add skip conditions to control the flow of Bamboo Stage execution

This feature will allow skipping any Stage of a Plan during execution Based on a condition. For example, when configuring a skip condition on a Stage, users can have something like these: "If the branch name is 'test_branch', skip this Stage", "If it's 9am to 6pm now, skip this Stage", "If the Plan is triggered manually, skip this Task".

Skip this Stage based on:

1. time interval
2. how the Plan (and therefore the Stage) has been triggered
3. who triggered the Plan/Stage (list of user names or groups)
4. who committed changes to the Configured Repositories for this Plan(Stage)
5. what branch is running the Stage (the user can specify a list of branch names, or set a regular expression)
6. the Agent or Environment (user can specify the agent name)

(This list can be expanded)