Remove unnecessary code
Move video start outside of foreach because we cannot return from it

This prevents the video from being started several times is some cases
Implement IE emulation for www.youtube.com by sending the IE 10 user-agent

The MetroUI Internet Explorer on Windows 8 does not offer Flash and so youtube
has to offer their videos as html5 for it.
At the moment it is sufficient to send the IE10 user-agent, but in the future
some javascript modifications may become necessary.

This is based on a review by Raylan Givens on mozilla addons.
Remove red flash-not-found alert bar

This confuses users that installed the addon, browse to youtube and see the error
message (although the videos work fine). So remove it using page-mod and a simple
css file.
Remove autostart

Autostart no longer makes sense when the emulate IE setting will become the
default, because it always autostarts.
Move the emulate IE setting into the video-loading methods as new default

Having two seperate settings is confusing.
The button now serves as a fallback, if youtube decides to drop IE support.
Make addon work when click_to_play is enabled

(patch by Alexander Schlarb <alexander4456@xmine128.tk>, slightly modified by Klemens Schölhorn)
Merge in support for firefox's click_to_play

This removes the flash plugin from the list of supported plugins in javascript
(navigator.plugins), so youtube thinks there is no flash available.

Patch by Alexander Schlarb <alexander4456@xmine128.tk>,
modified by Klemens Schölhorn <klemens@schoelhorn.eu>