Remove configuration option for flash plugin name

This is no longer needed since we will use a different method for disabling flash
soon.
Remove possibility to move the button to the navigation toolbar

This is no longer needed with the new ActionButton api in australis. (And it never
really worked anyway)
Fix whitespace
Switch to australis button api and sdk-widget for older firefox versions

Use the new ActionButton api in australis for the button and fall back to
the classic sdk-widgets for firefox versions below 29.
Both versions now use svg graphics instead of the old bitmap ico ones.
This commit also removes the notification if flash is not installed.
Reduce size of svgs by stripping unneeded inkscape attributes
Use pref system directly to get flash status and clean up code

We now use the pref "plugin.state.flash" directly to get and set the status of the
flash plugin and to listen for changes. This is necessary if we want to support
click_to_play in the future, because although the PluginHost api supports it,
the AddonManager, which is used for change notifications, does not support it.

The new code was bundled in the module PluginStateManager. Therefore the existing
very ugly code using the PluginHost could be completely removed.

This results in a overall code reduction in the main module from 228 to 82 lines,
which hopefully will make maintenance and new features much easier in the future.
Bump version to 1.0.0beta1