Fix Save Preview As... for textures, now save as any type we can encode to!

Removes the previous method and condenses the menu entries back into one.
 - Translations have been updated except for German, German will need to update the translation for "Save Preview As..." since the name hasn't changed.
Adds FFSAVE_IMAGE to the filepicker enums
Crossplatformity:
 - The Windows version works nicely
 - The Linux version may not work or even compile but it should..
 - The Mac version hasn't been added, instead it will default to accept any(all filter), should the provided file extension be invalid a notification will display.

indra/llui/llfloater.h

@@ -218,7 +218,6 @@ public:
 	virtual BOOL	canSaveAs() const { return FALSE; }
 
 	virtual void	saveAs() {}
-	virtual void	saveAsType(BOOL type=false) {}
 	
 	void			setSnapTarget(LLHandle<LLFloater> handle) { mSnappedTo = handle; }
 	void			clearSnapTarget() { mSnappedTo.markDead(); }