[ML][pipeline] Implement Pipeline::dispose()

[ML][pipeline] Implement Pipeline::dispose()

ACR: TWDAPI-274

[Verification] Tested in Chrome DevTools with the snippet below, works
fine.

var pipeline = tizen.ml.pipeline.createPipeline('videotestsrc ! tizenwlsink',
                                                function(state) {console.log(state);})
// test screen appears

pipeline.dispose() // no errors, test screen disappears

Change-Id: I5401c3210f73619d5577380abf17139fadc390f1
Signed-off-by: Pawel Wasowski <p.wasowski2@samsung.com>