Merge with custom_chewie plugin

[cbenhagen]

Let's merge back the features of the custom_chewie plugin. Unless there are very good technical reasons I don't see the point of having two very similar plugins that even have almost the same name.

We recently did a major refactor of the code which should make it much easier to customise things. #100 tracks the effort to make customising more end-user friendly.

@bostrot, what do you think? Would you want to collaborate on this?

[bostrot]

Thats true. There isnt even a point in the other plugin. Unfortunately I don't have much time at the moment for a rewriting for a pull request.
Though I would really like to cooperate on this one.

[cbenhagen]

Guess you could start by creating issues for features that need to be merged. With a quick description and if you have, some information about things to keep in mind when implementing. I can then try to do them and ping you if I need assistance. As soon as those are all fixed we can add a notice to the README of your fork and push that to pub. Deleting from pub is not possible as far as I know.