Make a file level dependency between aui.toolbox and build/aui.views/shaders and buid/aui.views/assets

[Alex2772]

Changes to aui.toolbox does not force CMake to regenerate temporary build files produced by aui.toolbox.

Recent change #613 raised this issue again.

Steps to reproduce

1. Clone AUI and checkout a version prior to recent aui.toolbox changes (i.e., v8.0.0-rc.9)
2. Build and run aui.example.views
3. Observe that aui.example.views works perfectly fine.
4. In the same source tree, checkout a version after recent aui.toolbox changes (i.e., v8.0.0-rc.11)
5. Build and run aui.example.views. Note: do not change or clean up build directory
6. Observe aui.example.views fails to initialize shaders, due to the fact they didn't regenerated. (See OpenGL errors in #628)

This must be fixed in both AUI repo itself and projects using AUI (i.e., example_app).