In some cases (due to network issues), the webcam video can be shorter
than the time between the start/stop events. Pad the input video with a
blank video to make sure that there's input to the video tiling filters,
to fix a problem where the video won't render correctly with ffmpeg v3.4
and later.

[AIR] Stop the active poll when the result is shown

Implement new polling popup

# Conflicts:
#	clients/flash/air-client/src/org/bigbluebutton/air/main/views/MenuButtons.as

Use PNG slides for iOS

Cleanup AIR settings

 - generate png files for uploaded presentation

User inactivity timer

Mobile lock settings

[AIR] Add background for TopButtons and chat's SendButton

[AIR] Update participants sort

Bump AIR version from 28 to 29