Minor cleanup: make data members in LLViewerMediaImpl private.
Minor cleanup: make data members in LLViewerMediaImpl private.

This required adding one accessor and making two related classes friends of LLViewerMediaImpl.

gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm