common: Add messages for handling global IO limits

This patch adds LIZ_<MATOCL|CLTOMA>_IOLIMIT* messages that will be used
in the global IO limiting mechanism. It also adds some tools that were
needed to implement these messages, concerning serialization and unit
testing.

Closing #152
common: Fix string and vector<string> seralization

There was a bug in serialization of std::string and
std::vector<std::string>, which (depending on an architecture) may led
to serializing field length as a 64 bit variable, while it was always
deserialized as a 32 bit variable.