jpegparser: Rewrite element
Now it uses the JPEG parser in libgstcodecparsers, while the whole code is simplified by relying more in baseparser class for tag handling.
The element now signals chroma-format and default framerate is 0/1, which is for still-images.
Fixes: gst-plugins-bad#1690 (closed), gst-plugins-bad#140 (closed), gst-plugins-bad#217 (closed)