Create the Rails-related database rake tasks

We should provide meaningful replacements for the default database related rake tasks (that is everything under the `db`-namespace). This ensures compatibility with exiting tools (i.e. Capistrano). At the same time this means we do not need a replacement for every tasks. In that case just implement a `noop`.

For further reference take a look at the [implementation of mongoid][1].

**Note**: The current implementation uses some nifty monkey patching to make up for yet missing features in [Ashikawa::Core](https://github.com/triAGENS/ashikawa-core/issues/83). As soon as the features have been added to Ashikawa::Core this monkey patch **must be removed**. _Removed_ as this:

![b04](https://cloud.githubusercontent.com/assets/1948/2877341/50c39026-d449-11e3-8aca-64613d85f3d4.gif)

**ProTip™**: It should be enough to revert commit 129ebe41ed9e823990de62f0a3cf3eb4965aa26d.

[1]: https://github.com/mongoid/mongoid/blob/master/lib/mongoid/railties/database.rake