Somewhat refactored IRCBox::Message.

_attributes has been replaced by individual fields.
_type and _sender have been made static and renamed to _typeRegexes and
_senderRegexes, respectively.
_typeRegexes is now a vector.
Removed the default value from Message::Message(std::string) (clang was
complaining).
Message::get returns a const reference.
Message::get returns _value by default.
Added a trim function that hopefully replaces Toolbox.hpp's.
Removed #include "Toolbox.hpp"