Added support for exit portals

Fixed rendering presets in Settings Editor
Added menu item to manually change location for LuxRender

Fixed loading of sketchup scene by double-clicking on it. Now materials get exported correctly

Implemented materials now support image maps on every channel

Set up skeleton for saving UV coordinates for the selected faces to use for texture channels when no texture is applied in Sketchup

Improved speed for checking is a face texture is distorted

Created Texture Editor, showing default parameters values and the ability to open and show an image to assign to diffuse channel
Settings and Material editors show scene parameter values when Sketchup opens by double clicking on a .skp file
Small changes to material parameters names

All implemented materials are exported without errors
Eliminating checks for distorted textures speeds up exporting process
UV coordinates are exported for all geometries

Disabled Sketchups' observers when launching scene export.
Creation and deletion of observers grouped inside module methods.

Improved Material Editor performances eliminating unnecessary GUI updates
Cleaned up code for writing LuxRender material file