encodebin: Expose more specific sink template caps.

Submitted by Mathieu Duponchelle @meh

Link to original bug (#751475)

Description

Having STATIC_CAPS_ANY on both templates led to issues
in gst-launch with such a profile:

application/ogg:video/x-theora:audio/x-vorbis

ie one audio and one video encoding profile, both with no
presence.

This led gst_element_request_compatible_pad (gst-utils.c)
to return either template, which was not necessarily compatible.

The reason for having STATIC_CAPS_ANY was to allow for
"avoid-reencoding", however there only is a small set of formats
that can be directly remuxed, we thus specify them all
in the video template caps.