mp: Use Title Case for replay mode combo box items, rename an item

"Normal" was meant to be "Normal Replays" (and it is so in master), but
at the time the combo box was introduced, the author couldn't use
strings that weren't already present in the translation catalogues due
to the 1.11.10 - 1.12.0 string freeze.

src/multiplayer_lobby.cpp

@@ -873,9 +873,9 @@ lobby::lobby(game_display& disp, const config& cfg, chat& c, config& gamelist) :
 	search_string_(preferences::fi_text())
 {
 	std::vector<std::string> replay_options_strings_;
-	replay_options_strings_.push_back(_("Normal"));
-	replay_options_strings_.push_back(_("Quick replays"));
-	replay_options_strings_.push_back(_("Enter blindfolded"));
+	replay_options_strings_.push_back(_("Normal Replays"));
+	replay_options_strings_.push_back(_("Quick Replays"));
+	replay_options_strings_.push_back(_("Enter Blindfolded"));
 
 	replay_options_.set_items(replay_options_strings_);