Replace getopt_long_only with getopt_long

It seems that in the past, the intention was to only use long options.
At some point short variants where added, implemented as long options.
This patch cleans up the implementation and uses getopt_long that allows
parsing of both long and short options improving readability.

Signed-off-by: Olliver Schinagl <o.schinagl@ultimaker.com>
Fix output_viewer plugin (multiple compile issues)

The output_viewer plugin wasn't compiled in a while it seems because it
did not function. This patch fixes the compiler and linker issues
(ldflags needs to be on the end for some reason).

There is still a memory leak, as the viewer starts, displays the feed
for a few seconds, and then segfaults. TODO ;)

Signed-off-by: Olliver Schinagl <o.schinagl@ultimaker.com>
Fix compiler warnings on output_rtsp

This patch fixes compiler warnings for the output_rtsp plugin. The
plugin appears to be working normally, but cannot test at this time.

Signed-off-by: Olliver Schinagl <o.schinagl@ultimaker.com>