Move C4ComponentHost::LoadEx to C4Language

To make C4ComponentHost more reusable, move C4Language dependencies out
of the class.
LoadEx isn't really suited to reside in C4Language, but it's better to
have it there, since all C4Language consumers also use C4ComponentHost;
the reverse isn't true.
Move system string table to C4LangStringTable

libc4script requires the system string table, but doesn't require the
full-fledged C4Language. Move the table to C4LangStringTable to reduce
dependencies.
website header changes