Implement player events

Change-Id: I20275424cfb4261f031c9e22c674bd10009bfe1b
PlayerEndpointImpl: Use a function to adapt between lambda and C pointers

Change-Id: I4a30b278e36072563393cc7f74e37fd1e48ddf47
Implement event subscription system

Change-Id: I64a3219efb78fa3cd3e5b54f9c987fff246eed56
Forward errors to parent

Change-Id: I635c1ac9369e1e018c32c2e39f9474567caefe5b
Implement chroma filter

Change-Id: I88c85530ca3445743eb8eb484b4a2613d2a9a7bd
Implement FaceOverlay element

Change-Id: I2cd6e384ce5bdd9c505709643eef90dd43d2c2b1
Implement GstreamerFilter

Change-Id: I85d80631c9a8d52ae05bbca17420d3ec531e5622