* Added a new module FindSanitizers with new function add_sanitizers to combine
all sanitizers in one function instead of adding each one by one.
* Code of FindASan.cmake was outdourced into helper functions, so that the code
may be used by other sanitizer modules, too.
* AddressSanitizer will be used with -O1 now to get a better performance.
* removed build type ASAN. Targets should define ASan usage by sanitize_address
function
* compiler flags will be searched by compiler instead of per language
* FindASan warns, if a target can't be sanitized because of incompatible
compilers
* added some helper functions
