[SenateFloorGranicus] Add new extractor

[galgeek]

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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

A new extractor enabling download of US Senate videos linked from https://www.senate.gov/floor/ and hosted by granicus.com.

This PR addresses recent comments at issue #13399.

[johnhawkinson]

http://archive-media.granicus.com:443/ really? I mean, yes, that does seem to be true, but it also seems like an error that is likely to be corrected in the near future, thus breaking anything that depends on it…

[galgeek]

That's the host documented in this stack overflow from a year ago... admittedly odd!
https://stackoverflow.com/questions/51748091/download-video-from-granicus

http://archive-media.granicus.com/ works, too, now, in a browser window, but test/test_download.py TestDownload.test_SenateFloorGranicus* fails for me without :443:

$ python3 test/test_download.py TestDownload.test_SenateFloorGranicus_1
[SenateFloorGranicus] None: Downloading webpage
[info] Writing video description metadata as JSON to: test_SenateFloorGranicus_1_senate_ff605d76-86c3-4e8d-9991-9f32efd782de.info.json
[debug] Invoking downloader on 'http://archive-media.granicus.com/OnDemand/senate/senate_ff605d76-86c3-4e8d-9991-9f32efd782de.mp4'
[download] Unable to resume
[download] Destination: test_SenateFloorGranicus_1_senate_ff605d76-86c3-4e8d-9991-9f32efd782de.mp4
[download] 100% of 234.00B in 00:00
F
======================================================================
FAIL: test_SenateFloorGranicus_1 (__main__.TestDownload):
----------------------------------------------------------------------
Traceback (most recent call last):
  File "test/test_download.py", line 225, in test_template
    format_bytes(got_fsize)))
  File "/Users/bara/Dev/ytd/youtube-dl/test/helper.py", line 249, in assertGreaterEqual
    self.assertTrue(got >= expected, msg)
AssertionError: False is not true : Expected test_SenateFloorGranicus_1_senate_ff605d76-86c3-4e8d-9991-9f32efd782de.mp4 to be at least 9.77KiB, but it's only 234.00B 

----------------------------------------------------------------------
Ran 1 test in 1.088s

FAILED (failures=1)

I pushed up a small change to VALID_URL to make it just a little easier to remove :443 from the url later, if and when we need to.

[galgeek]

The latest update generalizes URL regexes more. This should make it easier to copy and paste to create extractors for other organizations using granicus.com.

I wonder whether there's an even more general way to write this? I had no luck with a quick try at separate granicus and senate floor extractors.

[galgeek]

The current version of youtube-dl, 2019.10.22, remains unable to download the video at urls like https://floor.senate.gov/MediaPlayer.php?view_id=2&clip_id=3125

This PR, rebased on current master, continues to enable these downloads.