configure.ac: The OpenWebRTC GStreamer plugins install no pkg-config file

And they are only a runtime dependency, no build dependency.
build: Don't use -pedantic and -ansi

They will fail the build too easily with external headers and don't do what
one would expect. Instead let autoconf figure out the right compiler flags for
using a standard conformant C compiler.
nice: Version 0.1.7.1 or newer is required to build
owr_local_media_source: Work around wrong compiler warning

owr_local_media_source.c: In function 'owr_local_media_source_get_pad':
owr_local_media_source.c:119:10: error: 'source' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     if (!gst_element_link(a, b)) \
          ^
owr_local_media_source.c:296:17: note: 'source' was declared here
     GstElement *source, *capsfilter = NULL, *tee;
build: Requires gstreamer-app-1.0 and gstreamer-video-1.0 too
transport/owr_candidate: Use - instead of _ to prevent assertions with G_PARAM_STATIC_STRINGS
build: Fix linking of the bridge daemon
Require GStreamer >= 1.4 and write the version only once