Initial implementation of interceptors.

I'm anticipating implementing interceptors at two independent parts
of the API. The first is high-level interceptors, that intercept
before the socket connection has been established.

The second set of interceptors will only execute for requests that
require a socket connection. Those are forthcoming.
Merge pull request #1193 from square/jwilson_1207_interceptors

Initial implementation of interceptors.
Merge pull request #1196 from nfuller/SwitchOffSslv3

Change COMPATIBLE_TLS to be TLSv1.0 and not SSLv3
Remove NPN support from OkHttp

Work in progress.

I see a new failure from a certificate pinning test but I don't
know why. Help solving this would be appreciated.

I also see failures before & after:
1) A failure from DisconnectTest
(https://github.com/square/okhttp/pull/1197 may fix that).
2) A failure from CallTest.doesNotFollow21Redirects_Async (timeout)

The maven changes should be treated with the contempt they deserve.
I mostly removed things I didn't understand and stroked maven until
it stopped squealing. The benchmarks / okcurl changes are a
particular mystery.

Tried with arbitrary versions of openjdk7 and openjdk8 I had
lying around. Behavior was the same across both (i.e. the same
failures).
Adding TLS_FALLBACK_SCSV support

This is to upstream changes made in Android for
the POODLE vulnerability.