Add configurable known issues

[Laupetin]

This adds the feature to add known issues to the configuration that can be referenced by an alias.
This makes it possible to for example reference a commonly used ticket like one to book recurring meetings on without having to remember the ticket number.

This PR adds the new feature to the YAML format only for now since i am not familiar with the Buch format. If it also should be implemented there, let me know.

[BuJo]

Generally I like the idea.
I think it needs a little bit of time to think how it interacts with

• the way parsers are configured
  Top level configs and growing parameters to the initializers
• the way parsers interact with the data format, issue being a number normally
• It might be that the resolver infrastructure isn't good enough but might be the better place
• the way it would interact syntax wise with the idea of being able to enter times on projects instead of issues

[BuJo]

Let's tag this as hacktoberfest-accepted, as it basically could be merged just like this. However, the code surrounding this feature could be better integrated... Let's not rush this out the door just yet.

[Laupetin]

So the issue aliases now make use of resolvers, so they can be added optionally.
To make this work i had to move some of the features of the yaml parser to new resolvers to make the parser accept more input data that can then be resolved.

I did make these new resolvers be enabled by default to not make it so existing workflows no longer work without adding the new resolver via the configuration.
I hope that's an okay approach.

It might be a good idea to test whether this broke any existing workflows, i'm afraid i can only be sure about my own one.