Clean up the format list output

These changes are meant specifically for YouTube videos, but it might make things look a bit nicer for other IEs too. Things get a bit messy when using the DASH manifest, but no worse than they were before. I've half a mind to rewrite the whole damn `format_note()` function; it's confusing as hell and produces redundant output in some cases.

Here's a comparison:
```
[info] Available formats for dZ5-RcVIizU:
format code extension resolution  note
171         webm      audio only  DASH webm audio , audio@ 48k (worst)
140         m4a       audio only  DASH audio , audio@128k
160         mp4       144p        DASH video , video only
242         webm      240p        DASH webm
133         mp4       240p        DASH video , video only
243         webm      360p        DASH webm
134         mp4       360p        DASH video , video only
244         webm      480p        DASH webm
135         mp4       480p        DASH video , video only
247         webm      720p        DASH webm
136         mp4       720p        DASH video , video only
248         webm      1080p       DASH webm
137         mp4       1080p       DASH video , video only
264         mp4       1440p       DASH video , video only
100         webm      360p        3D
82          mp4       360p        3D
84          mp4       720p        3D
17          3gp       176x144
36          3gp       320x240
5           flv       400x240
43          webm      640x360
18          mp4       640x360
22          mp4       1280x720    (best)
```
```
[info] Available formats for dZ5-RcVIizU:
format code extension resolution  note
171         webm      audio only  DASH audio, audio@ 48k (worst)
140         m4a       audio only  DASH audio, audio@128k
160         mp4       144p        DASH video, video only
242         webm      240p        DASH video, video only
133         mp4       240p        DASH video, video only
243         webm      360p        DASH video, video only
134         mp4       360p        DASH video, video only
244         webm      480p        DASH video, video only
135         mp4       480p        DASH video, video only
247         webm      720p        DASH video, video only
136         mp4       720p        DASH video, video only
248         webm      1080p       DASH video, video only
137         mp4       1080p       DASH video, video only
264         mp4       1440p       DASH video, video only
100         webm      360p        3D
82          mp4       360p        3D
84          mp4       720p        3D
17          3gp       176x144
36          3gp       320x240
5           flv       400x240
43          webm      640x360
18          mp4       640x360
22          mp4       1280x720    (best)
```