EXT-7536 FIXED (Favorites bar and Navigation bar looks similar to the mock-up)

- Added constant FAVBAR_TOP_PADDING in the LLNavigationBar which defines the distance between navigation panel and favorites panel in pixels.
- Added new image NavBar_BG_NoFav_Bevel which is used to show navigation panel with favorites bar hidden. It is required to show navigation panel with bevel at the bottom.
- Added new image NavBar_BG_NoNav_Bevel which is used to show favorites panel with navigation panel hidden. It is required to show favorites panel with bevel at the top.
- Removed image NavBar_BG_NoFav. It is not used anymore.
- Modified the methods showNavigationPanel and showFavoritesPanel to take into account that distance.

Reviewed by Vadim Savchuk at https://codereview.productengine.com/secondlife/r/664/

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branch : product-engine