movenc: use 'hev1' tag for HEVC in MODE_MOV.

'hvc1' requires that parameter set NAL units be
present only in the samples entry, but not in the
samples themselves, requiring that additional
parameter sets, if present, be filtered out of the
samples and placed in new, additional sample entries
if they override or otherwise conflict with the
parameter sets present in the first sample entry.
We do not have any way of doing this at present, so
the files we produce can only comply with the
restrictions set for the 'hev1' sample entry name in
ISO/IEC 14496-15.
