Organizing Solobot directory into hierarchy of subdirectories.

The four immediate subdirectories to our game's asset directory now include:
 * **Scenes** - Currently only contains our one scene, now named `Main Scene`
   One may be all we need, maybe not.
 * **Materials** - We previously had both a **Textures** and **Materials**
   subdirectory, however, I feel that the **Textures** directory simple stored
   the images that were used in the materials. So it should itself be a
   subdirectory of the Materials directory. So if you have a texture you want
   to use in the game, you'll need to create a material with it. You'll do this
   by first importing the image via the Unity editor into the Textures folder.
   You'll then browse to or right click on the **Materials** subdirectory of
   our Solobot game directory. You can then right click or in the upper hand
   corner hit `Create` -> `Material`. You can then edit the texture component
   of that Material and select your image by browsing to it in the in the
   **Materials/Textures** subdirectory.
 * **Prefabs** - This subdirectories should not contain any Prefabs, but instead
   should contain a hierarchy of subdirectories that contain Prefabs, which
   prefereably only be completely finished objects, scripts included, that are
   ready to be dropped in the game.
 * **Scripts** - This should basically be a collection of all the scripts that
   are components of our game's Prefab objects. If we do this *right*, then
   everything in our game should end up blue in the project pane of Unity and
   everything should be in the **Prefabs** directory as a reusable pluggable
   object for any future projects any of us may do in Unity.