Fix devDependencies

[jeme]

Karma has changed so that a number of plugins are now required to be installed for Karma to run our tests.

Since there was some troubles in just adding those alone to the devDependencies they got added to the Travis build file instead.

However this won't reflect our devDependencies correctly so we need to fix this issue and while doing so we may as well also move to a local installation of Karma.