Check for requirements

[Tygre]

AmiModRadio should check for the required libraries at start-up and fails gracefully if some are missing (and, of course, tell the user what is missing!).

[Tygre]

AMR used to be totally silent when some library was missing because I was compiling it with the "auto" linker option. I now managed myself the libraries and can do some nice reporting if something is amiss!