fixed major EXT-6593 "New notifications arrived while you were away" is bold

and doesn't fit on toast
* Unbolded startup toast message text;
* Avoided increasing complexity of LLToastNotifyPanel class that in future
should be decoupled on separate independent toast panel implementations and
added LLPanelGenericTip class to represent generic notifytip panels.

reviewed by Vadim Savchuk and Mike Antipov at
https://codereview.productengine.com/secondlife/r/214/

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branch : product-engine