Client decides on Uncached/Cached query and update

[kzangeli]

Description

The new (as of August 2014) redirecting implementation makes all query/update ngsi10 requests a bit more accurate but also a bit slower (as providing applications are consulted - see issue #503).

Now, it would be nice to let the client decide the behavior of the broker, for example with a URL parameter.
The default would be this 'improved' behavior, but for a client that cares more about speed than about accuracy, it could be nice to be able to switch back to the previous behavior (using only the brokers local data and not contacting context providers for more accuracy).

This new URL parameter could be like this:

'cache=on'
'speed=true'
'consultProviders=false'
...