[FIX] Middleware: Allow usage without express server

[matz3]

This makes all middlewares independent of the express specific
req.path property by manually parsing the standard req.url.

The parseurl library is also used within express and makes sure to
not parse the same URL of a request object again by using a cache on
the request object.

Follow up of #184

Fixes: SAP/karma-ui5#64

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[coveralls]

Coverage increased (+0.08%) to 93.284% when pulling 6b36348 on fix-middleware-url-handling into 498cf6b on master.

[codeworrior]

LGTM.

When I made the change for the CSP middleware, I thought about an additional test without express to ensure the desired use case. But the necessary setup seemed to be quite complex, so I abandoned that idea.

If we have more scenarios than just the legacy grunt tooling, having such a test might make sense. What do you think?

[matz3]

I also thought about this. Currently most of the time we just mock the req/res objects and call the middleware directly. This should be fine as long as we don't provide other properties like path, which could be done wrong when introducing a new middleware.

So some integration tests with plain Node http, connect and express would be a good thing.