Add the ability to change git provider and send notifications about events

### About git providers
Could you tell me if there are any plans to add the ability to change the git provider? I know your codebase a little, but I can already see problems blocking this possibility. In my opinion it would be nice to change the git provider usage like this:

- Create interfaces that describe all the features of the git provider.
- Change the git provider related Github classes to interfaces.
- Add new providers: Gitlab, Bitbucket

This is quite a lot of work, so I would like to discuss the possibility of doing it. For my part, I will try to devote a little time to this on the weekends. I am interested in this update as I can use it to automate workflows at work.

### About notifications
I also wanted to discuss the possibility of adding a notification interface to be called after any action with git provider. It would be possible to wrap notification in decorator and send updates about the actions to, for example, Jira. This can even set in settings, and over time, the number of providers where you can send information about the event can be expanded. The easiest way to make it workable is to implement the first provider - webhook provider, that send json with information to url from settings like:
`{"action": "create release", "data": {"additional": "additional"}}`