Allow higher dependency versions than earlier.

Especially grunt-contrib-coffee 0.7.0 changed source map support but the
version was not allowed by our earlier requirements. The requirements
are now changed so that only the major version of a dependency is not
allowed to change.

At this point of the project it might be sensible to keep changing our
code to match any significant changes in the dependencies instead of
freezing on some unsupported version 0.1.2, for example.

To facilitate updating dependencies, the list has been moved from
devDependencies to dependencies because of a bug/feature in npm update:
https://github.com/isaacs/npm/issues/2369