* Use compile time detection of the YubiKey libraries and link against
the libraries if present. Can be disabled with:
$ cmake -DCMAKE_DISABLE_FIND_PACKAGE_YubiKey=FALSE
* A stub file provides empty calls for all the function calls integrated
in to the UI to support this. In the future a more modular approach
maybe better, but opting for simplicity initially.
Signed-off-by: Kyle Manna <kyle@kylemanna.com>