use newer, thread-safe BasicCookieStore

In production logs, we would frequently get ConcurrentModificationException in CBLHttpClientFactory.addCookies. Tracing the code for a potential concurrent modification was fruitless.

Updating to a more recent verion of Apache's BasicCookieStore that is newer than what Android provides and has been rewritten with better concurrency support stopped the issue from occurring.

(fixes couchbase/couchbase-lite-android-core#4)

(**Note:** having to inline the code & change the namespace on it is kind of unfortunate, but I'm not sure what else to do in this case. This was our second-highest incidence crash after couchbase/couchbase-lite-android#109 until we rolled out this change. Happy to help with improvements to the patch or another direction.)