EXT-7242 FIXED Added a new "Edit my Shape" link to avatar self-click context...

EXT-7242 FIXED Added a new "Edit my Shape" link to avatar self-click context menu and made it open the shape editing panel.

Again, as in EXT-7241, I tried to improve the way the appearance panels (outfits / edit outfit / edit wearables) are switched, this time aiming to eliminate redundant time-consuming operations (fetches/updated/etc).
I'm not particularly satisfied with the resulting code but it seems to work. A better solution might be to wrap the panels with LLSideTrayPanelContainer.

Additional minor changes:
- Fixed unsafe pointer cast in LLSidepanelAppearance::editWearable().
- Removed redundant onEditOutfitButtonClicked() and onEditWearBackClicked() methods from LLSidepanelAppearance.

Reviewed by Nyx at https://codereview.productengine.com/secondlife/r/395/

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branch : product-engine