record-and-playback: Forced alt to be included as part of the image thumbnail element in preview extension

record-and-playback: Filtered presentation files to provide only the first thumbnail for default.pdf

Logger was apparently imported by the matterhorn stuff ?! so move that
to the main library.

Fix a variable reference in sanity.

Instead of assuming that wav files have 44 byte headers (they usually
don't - freeswitch adds some metadata tags), add a super-simple wave
file parser that just finds the offset where the audio data actually
starts.

The sanity check script was using one of the functions; it's been
changed to use a function from the EDL audio code instead.

It's no longer used anywhere in the recording processing, and the one
remaining use in the sanity script can be replaced with a (less buggy!)
function from the video EDL code.

Use a function that handles parameters correctly when updating the
timestamp in the url for links, fix indentation in caption loading code.
Treat exceptions when checking for url existence as errors.

Main change is to rewrite the start/stop event handling to do fewer
passes and use simpler logic (it no longer has to track durations).

The temporary work audio codec is switched to flac; slightly lower hard
drive use and it avoids the 4-hour length limit of wav.

Some improvements to the video seeking when processing deskshare and
webcam videos, to avoid video dropouts.

Tweaks to the audio encoding quality settings.

Remove an unused function.

Right now the captions are only rendered if there's a video present. If
the meeting doesn't have a video (webcam or desktop sharing), we'll need
to just make up a blank one.

Wasn't binding to events in the proper order, causing cliks in a thumbnail
not to behave properly.

Bigger and more well spaced buttons, specially in small screens.
Also updated the colors to match the latest design definitions.

The event "loadeddata" is only triggered on firefox mobile once the
video/audio is played, so it requires the user to click on the play button
for it to be triggered.
The playback page was waiting for the event to be triggered before
removing the "loading" page, and that would never happen on firefox mobile.

Now we don't wait anymore for the video to be loaded, we just wait for
the slides and the initial setup.

Resize the slides after swapping presentation and video, so that it fits
the new region properly.

When swapping video and presentation now the presentation is updated
properly, before it would not show any slide until there was a slide
change.

Also added a few protections to prevent js code from breaking.