Decouple video start and video resize

We have to implement the size change separately because the new ie method no longer
expicitly starts the video.
Rename registerObserver() to startVideoOnError()

The new name does no longer describe the implementation but the purpose of the
method which seems far more logical
Remove started variable, because it was not used
Add funtions to show and hide the youtube html5 button

This is needed for full spf support.
Check if the error is already shown before waiting for it with an observer

This makes the funktion suitable for normal and spf mode.
Add helper function to check if the current page is a video page
Remove extra spf script and implement the logic in the main script

The main script is now included on all youtube pages and not only on video sites.
Therefore the button is dynamically shown or hidden after every page change.
Reenable automatic size change for non-playlist videos

This has been removed while separating video start and size change
Remove the transition of the suggested videos sidebar

This transition was just irritating when the automatic size change was applied.
Add option to disable spf

Although the add-on's code can cope with spf, it seems youtube sometimes cannot,
when flash is not installed. So add an option to disable it.
The default is currently to disable it, but that could change if youtube fixes its
problems.