Issue title: Compressed image topic not accessible
 Issue body: I have two compressed image topics that I am publishing. For example, one is at `/robot/cameras/bw/image_raw/compressed`. I verified that the topic is subscribed to by `/web_video_server` by checking `rqt_graph`. 

When I visit http://localhost:8080, I can see the two camera topics listed without any links to click on to navigate to the stream or image snapshots.

Both image topics have camera_info additionally being published, and if I publish the raw_image without compression it seems to work fine.
 Comments: 
 Comment 0: Still seems to be an issue at this time. I have a `CompressedImage `stream at `/raspicam_node/image/compressed` yet no topics are listed at localhost and trying to access it at say:

`http://localhost:8080/stream?topic=/raspicam_node/image&type=ros_compressed`

or 

`http://localhost:8080/stream?topic=/raspicam_node/image/compressed&type=ros_compressed`

gives nothing.

But given that most of the documentation seems to focus on compression instructions I guess this server doesn't even support publishing pre-compressed messages and merely accepts raw to compress and send. Kind of a bummer though.
 Comment 1: any updates on this issue? I'm having the same issue
{'source': 'GithubIssues', 'repo_name_with_owner': 'RobotWebTools/web_video_server', 'issue_id': 494795611, 'repo_stars': 210.0}