Change naming convention, merge texture/shaders

Reduce the number of files in project by merging texture and shaders into
assets/renderer file. It's better to keep code local to where it is rather than
splitting them into "self-contained modules". It becomes easier to understand
reading top-to-bottom and there's is less jumping around which can increase the
difficulty of comprehending the code.

Convert names to use more of a <namespace>_<object><Action> format.

Dengine.vcxproj

@@ -130,10 +130,8 @@
     <ClCompile Include="src\MemoryArena.c" />
     <ClCompile Include="src\Platform.c" />
     <ClCompile Include="src\Renderer.c" />
-    <ClCompile Include="src\Shader.c" />
     <ClCompile Include="src\String.c" />
-    <ClCompile Include="src\UserInterface.c" />
-    <ClCompile Include="src\Texture.c" />
+    <ClCompile Include="src\Ui.c" />
   </ItemGroup>
   <ItemGroup>
     <None Include="data\shaders\default.frag.glsl" />
@@ -155,10 +153,8 @@
     <ClInclude Include="src\include\Dengine\Math.h" />
     <ClInclude Include="src\include\Dengine\OpenGL.h" />
     <ClInclude Include="src\include\Dengine\Renderer.h" />
-    <ClInclude Include="src\include\Dengine\Shader.h" />
     <ClInclude Include="src\include\Dengine\String.h" />
-    <ClInclude Include="src\include\Dengine\Texture.h" />
-    <ClInclude Include="src\include\Dengine\UserInterface.h" />
+    <ClInclude Include="src\include\Dengine\Ui.h" />
     <ClInclude Include="src\include\Dengine\WorldTraveller.h" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />