added first version of a thread-safe event queue class

- based on an example given in iX Dossier "Einstieg in C++11"
- work towards issue eudaq/eudaq#35
added new exception type 'MutexLockException'

- used in thread-safe event queue
- work towards issue eudaq/eudaq#35
started work toward replacing std::queue with a thread-safe version

-work towards issue eudaq/eudaq#35