Add CouchbaseLiteListener.framework to couchbase-lite-ios.podspec

This adds `CouchbaseLiteListener.framework` to `couchbase-lite-ios.podspec` which should hopefully be all that's needed for https://github.com/couchbase/couchbase-lite-ios/issues/39#issuecomment-27607889.  At least on the iOS side.

This is what I modified for locally testing this podspec.
https://github.com/davidquon/Grocery-Sync-iOS/tree/cocoapod_test_v2

My apologies for the back-to-back pull requests.  I wasn't sure how hard it was going to be to get the CouchbaseLiteListener.framework included and I wasn't sure how long the PR process was going to take so I want to make sure I got in the part that I needed.  Luckily it was as easy as I had hoped.  :wink: