Transitive dependencies (closes #238)

Use and provide transitive dependencies.

Rely on glbinding with its includes and libraries, so that no OpenGL linking is required.
Include GLFW and glbinding in own includes and libraries when using the globjects find script.

The only drawback is the GLFW find script, which is expected to exist in a location searched by cmake.
Unfortunately, the cmake subdirectory of globjects isn't.
I don't know if we should add the cmake directory if the find script from the project root is used and install the glfw find script for system-wide usage.
Another possibility is to add a GLFW find script to either the cmake find script repository or the GLFW project directly.
Opinions required.