Media agent for iOS v4.1.4

Published to CocoaPods

• NewRelicVideoAgent 4.1.4
• NRAVPlayerTracker 4.1.4
• NRIMATracker 4.1.4

Bug fixes

• Exposed sendSeekStart/sendSeekEnd on NRVAVideo; auto-detected seek in AVPlayerTracker (34493b4)
• Fixed NRTrackerPair leaking NSNull sentinel to callers (82ef94f)
• Implemented partial container sanitization, nil guard, and dead code removal (6aac79f)
• Read totalPreRollAdTime from CONTENT_START attributes (d565378)
• Sanitized attribute values at setAttribute storage boundary (7d07298)