Internal renaming of elder,leader,regular,basic to numbers

Changed internals so trust levels are referred to with

TrustLevel[1], TrustLevel[2] etc.

This gives us much better flexibility naming trust levels, these names
are meant to be controlled by various communities.

app/services/spam_rule/auto_block.rb

@@ -18,7 +18,7 @@ class SpamRule::AutoBlock
 
   def block?
     @user.blocked? or
-      (!@user.has_trust_level?(:basic) and
+      (!@user.has_trust_level?(TrustLevel[1]) and
         SiteSetting.num_flags_to_block_new_user > 0 and
         SiteSetting.num_users_to_block_new_user > 0 and
         num_spam_flags_against_user >= SiteSetting.num_flags_to_block_new_user and

app/services/staff_action_logger.rb

@@ -17,8 +17,8 @@ class StaffActionLogger
 
   def log_trust_level_change(user, old_trust_level, new_trust_level, opts={})
     raise Discourse::InvalidParameters.new('user is nil') unless user and user.is_a?(User)
-    raise Discourse::InvalidParameters.new('old trust level is invalid') unless TrustLevel.levels.values.include? old_trust_level
-    raise Discourse::InvalidParameters.new('new trust level is invalid') unless TrustLevel.levels.values.include? new_trust_level
+    raise Discourse::InvalidParameters.new('old trust level is invalid') unless TrustLevel.valid? old_trust_level
+    raise Discourse::InvalidParameters.new('new trust level is invalid') unless TrustLevel.valid? new_trust_level
     UserHistory.create!( params(opts).merge({
       action: UserHistory.actions[:change_trust_level],
       target_user_id: user.id,