Use wide_to_utf8 and utf8_to_wide instead of wide_to_narrow and narrow_to_wide at almost all places.
Only exceptions: test functions for narrow conversion, and chat, which is done in a separate commit.
Previously, m_proto_ver was set to the serialisation version
inside the legacy init packet.
Now, if the server doesn't send a protocol version (protocols < 25),
we set m_proto_ver to some value < 25 and > 0.
Adds everything needed for SRP (and everything works too),
but still deactivated, as protocol v25 init packets aren't final yet.
Can be activated by changing the LATEST_PROTOCOL_VERSION header to 25
inside networkprotocol.h.
