Upgrade to newer Bitbucket API and remove deprecated classes

[christiangalsterer]

[raspy]

I would postpone implementing this as long as line 4.x did not reach end of life. There is no point in dropping 4.x line support if possible, especially since this line is probably still widely deployed in enterprises, where it's not that easy to upgrade.

[hogarth-sv]

Is this the reason that #52 is an issue?

Feels like a 4.0.0 release dropping the 4.x support now that 6.x is out makes sense then ...

[ar613]

Yes, the plugin needs significant rework to use the new plugin API in Bitbucket 6. Is the project still alive? Last commit was almost a year ago.