textures and shader can now be created context independently.

used for screenshots and resizing currently

the name will soon be used for wrapping shader variables

- added `glDrawBuffers` call when creating fbo
- moved a clear color after actually binding the fbo to clear
- added r16ui pixel format
- getting the gl_format for a pixel format now also returns the type of
  cpu-side data (i.e. GL_UNSIGNED_BYTE)
- added adjusting the GL_UNPACK_ALIGNMENT and GL_PACK_ALIGNMENT if
  necesarry
- into_data for textures uses glGetTexImage
- moved renderables to extra files renderable.h and renderable.cpp
    - renderables have a unique id and can be retrieved by knowing this
      id
    - renderables have callback function for clicking and area
      selecting them
    - renderables can specify if they write their id or not (not fully
      working)
- made some update_uniform public
- added some uniform code for textures
- basic code to test pixel perfect hitboxes

…ding pixel data; refactor clicking demo

 - id extraction is now independent of endianess
 - using full 16 bits of written id value

… begin work on meshes

…tCreator recognize them