added a filtering-feature to test the api/v2

added json_spec to get some handy matchers to test the api; added a
feature that tests, if the filters throw out the expected work-packages.
now filtering for multiple types.
added some simple benchmarks to make sure that we are actually faster when we filter.
added a feature to test for the re-wiring of filtered parents

also refactored the examples to get more focused examples for the tests.
filtered work_packages are now rewired: children, that are not present in the filtered set are removed, parents are rewired to the first ancestor that is not filtered
fixing the ancestor-chain, adding tests on removed children
Adds support for server-side filtering of types.

Types (formerly planning element types) are now filtered on the server.
This allows for some performance gain when not traversing work packages
(formerly planning elements) on the client unneccessarily. This speeds
up both the client side filtering process as well as network transfer.
Removes client-side filter for types.

This removes the client-side filter for types (formerly planning element
types) in favor of the previously enabled server-side filter.
Replacing the ancestor-lookup(which hits) the database, with a lookup
that only hits on the already loaded work_packages.
Replacing arel-call with query: This opens up a default way to
specify&mix various filters.
Changed the parameters to use the conventions of query

You can now pass in arbitrary parameters using the syntax describe in
query. Parameters are transported via get, so this may lead to problems
when there are too many parameters - on the bright side: Things here
are not worse than in the queries-controller, which suffers from the
same issues.