better onload handling

This patch improves the way the window.oninit JavaScript function is
called. This function is used to initialiaze all JavaScript funcions
attached to the DOM so it needs to be executed **after** the full DOM
was parsed by the browser. Unfortunately currently only Mozilla supports
a DOMContentLoaded event. In all other browsers we had to wait for
the window.onload event which will only be called after **all** content
(including images) was loaded - this caused a visible delay on all
JavaScript generated content (like the toolbar) in non-Mozilla browsers.

Dean Edwards now presented a solution [1] which will work for all the bigger
Browsers and is used in this patch.

The following browsers now should fire the init event right after parsing
the DOM:

All Mozilla based browsers
Internet Explorer
Safari
Opera >

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