R1:0507626f01e5

Accept Conduit tokens as an authentication mechanism

Summary:
- Ref T5955. Accept the tokens introduced in D10985 as an authentication token.
- Ref T3628. Permit simple `curl`-compatible decoding of parameters.

Test Plan:
- Ran some sensible `curl` API commands:

```
epriestley@orbital ~/dev/phabricator $ curl -g "http://local.phacility.com/api/user.whoami?api.token=api-f7dfpoyelk4mmz6vxcueb6hcbtbk" ; echo
{"result":{"phid":"PHID-USER-cvfydnwadpdj7vdon36z","userName":"admin","realName":"asdf"…