Disable client state in OpenGL example after rendering. ...

Using the example code in another application that has other rendering
code can cause rendering bugs or memory access errors if client state
is not disabled.

Converted all Tabs to Spaces (git diff -w shows an empty diff)

Tidying up example applications so it looks easier to just grab code

Fixed scissoring in OpenGL example

OpenGL example now use the fixed function-pipeline. Code down by 120 lines.

Simplified ImDrawList system (samples are 20 lines shorter) + merged title bar draw bar.

Portability fixes to OpenGL example application (courtesy of djoshea)

Tidying up example applications

Tidying up example applications

Commented samples and shuffled bits of the initialisation based on user's feedback.

Added PixelCenterOffset for OpenGL/DirectX compatibility.

Added OpenGL and DirectX9 example applications