Make it easier to add Textures to Materials

Any property that expects a Texture component should be able to accept any image file.  Right now the property editor expects that the Texture components already exist, but if they don't it is non-intuitive to have to create one and then set a texture.  Make it possible to just specify an image, and if a Texture component doesn't exist, then just create one.

From the user perspective Textures are just Images by default. Yes Textures are more flexible than just images, but 90% of the time the user will just want to add an Image so make that easy.