Migrate to AbstractStatusChecksProperties class.

[XiongKezhi]

The current interface StatusChecksProperties is incompatible for future changes (e.g. #51), so this PR migrates to AbstractStatusChecksProperties (although the default method can be used, since the implementation is still in our control, we'd better refactor it).

In order to make the migration smooth without breaking the compatibility (if necessary), here is the plan or some steps for it:

1. deprecate the StatusChecksProperties interface and add the AbstractStatusChecksProperties class (this PR)
2. change BuildStatusChecksPublisher to allow it accepts implementations for both the old interface and new abstract class
3. release the checks api plugin with this PR
4. refactor the GitHub implementation GitHubStatusChecksProperties to extend AbstractStatusChecksProperties
5. release the github checks plugin with the refacotring in (4)
6. wait for some time to ensure the updating by users and then remove StatusChecksProperties interface