Add a Gitter chat badge to README.md

Replace deprecated calls in OpenCVFaceRecognizer

This will replace deprecated calls and stop calling the entire OpenCV backend as static.

* Fix null check for TimeUnit in IPCameraFrameGrabber (issue #411)

 * Add more appropriate default pixel formats for JPEG formats in `FFmpegFrameRecorder` (issue #410)

 * Optimize `AndroidFrameConverter` a bit

 * Support `AVPacket` in `FFmpegFrameGrabber` and `FFmpegFrameRecorder` to copy without re-encoding (issue #93)

eliminate individual get/put calls as much as possible

 * Add new `PrincipalComponentAnalysis` sample

 * Upgrade `OpenCVFrameRecorder` to use the new C++ `VideoWriter` API

Remove code in Frame.java that should never have been checked in

 * Upgrade `OpenCVFrameGrabber` to use the new C++ `VideoCapture` API (issue #357)

Fix IPCameraFrameGrabber incorrectly reading some headers

Some cameras send the header with a different case than
the IPCameraFrameGrabber was expecting.

Related https://github.com/WPIRoboticsProjects/GRIP/pull/532

Add `CaffeGooglenet.java` sample for the `opencv_dnn` module