copy DefinitelyTyped definitions to our repo

[xi]

depends on #2137

We are currently installing DefinitelyTyped with bower. This has some major drawbacks:

• It contains definitions for over 1500 projects. We only use 5. Downloading everything is really not required.
• The project is active, but not exactly fast when it comes to contributions. There are currently over 400 open pull requests and over 600 open issues. So if there is a bug, you may have to wait a long time before an upstream fix is merged.

For these reasons I propose to just add the relevant definition files to our repo. This would allow the following workflow:

• fix a bug locally
• create an upstream pull request
• update our copy from DefinitelyTyped once in a while (you may have to manually port local changes)

[der-john]

works.