more tweaks

- join: check if already member
- leave: checks if user is in given faction at all
- kick: early abort if no player provided
- create: early abort if no faction or password are provided
- create: use get_player_factions() instead of get_player_faction()
- create: reduce explicit nil checks
- disband: early abort if missing password
- disband: reduce param-count-checks and use table.getn()
- info: reduce explicit nil checks and use table.getn()
- passwd: early abort if no password provided
- in general remove explicit nil-checks where not needed

locale/template.txt

@@ -74,3 +74,6 @@ You cannot kick the owner of a faction, use '/factions chown <player> <password>
 
 You cannot leave your own faction, change owner or disband it.=
 No factions found.=
+You aren't part of faction @1.=
+You are already in faction @1.=
+