fixed EXT-6848 Avoid creation of dummy objects in LLOnlineStatusToast and...

fixed EXT-6848 Avoid creation of dummy objects in LLOnlineStatusToast and LLPanelGenericTip classes.
* decoupled tip toast panel related logic from class LLTast;
* moved documentation comment of  LLPanelGenericTip constructor from .cpp to .h file;
* corrected name attribute in panel_generic_tip.xml;

reviewed by Mike Antipov and Vadim Savchuk at https://codereview.productengine.com/secondlife/r/230/

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branch : product-engine