fix an uncaught bad lexical cast exception

coverity reports that it is uncaught and would therefore crash
the server if it occurred
replace many lexical_cast with lexical_cast_default

This is to avoid bad_lexical_cast exception. I'm not sure if in
any cases this could actually have thrown but it's better to be
safe.

Conflicts:
	src/server/game.cpp
catch boost::bad_function_call exceptions in server command handler

Don't know if this can actually happen in practice but it is
reported by coverity.
backport: change server to use utf8 instead of utils unicode

This is to make it easier to cherry-pick the exception catch fixups
server: catch invalid utf8 exceptions

issue reported by coverity