Rework application configuration

Use a preinitializer to load the settings from application.yml so
that they are available as early as possible. All settings can also
be overridden using environment variables.

The ad-hoc settins in environment.rb are then moved to this new
system so we have one consistent location for settings.

app/models/node.rb

@@ -58,7 +58,7 @@ class Node < ActiveRecord::Base
  
     find_by_area(min_lat, min_lon, max_lat, max_lon,
                     :conditions => {:visible => true},
-                    :limit => APP_CONFIG['max_number_of_nodes']+1)  
+                    :limit => MAX_NUMBER_OF_NODES+1)  
   end
 
   # Read in xml as text and return it's Node object representation

app/models/notifier.rb

@@ -105,7 +105,7 @@ private
   end
 
   def from_header(name, type, id, digest)
-    if domain = APP_CONFIG['messages_domain']
+    if domain = MESSAGES_DOMAIN
       from quote_address_if_necessary("#{name} <#{type}-#{id}-#{digest[0,6]}@#{domain}>", "utf-8")
     end
   end

app/models/spam_observer.rb

@@ -8,7 +8,7 @@ class SpamObserver < ActiveRecord::Observer
     when record.is_a?(DiaryComment): user = record.user
     end
 
-    if user.status == "active" and user.spam_score > APP_CONFIG['spam_threshold']
+    if user.status == "active" and user.spam_score > SPAM_THRESHOLD
       user.update_attributes(:status => "suspended")
     end
   end

app/models/user_block.rb

@@ -5,7 +5,7 @@ class UserBlock < ActiveRecord::Base
   belongs_to :creator, :class_name => "User", :foreign_key => :creator_id
   belongs_to :revoker, :class_name => "User", :foreign_key => :revoker_id
   
-  PERIODS = APP_CONFIG['user_block_periods']
+  PERIODS = USER_BLOCK_PERIODS
 
   ##
   # returns true if the block is currently active (i.e: the user can't

app/models/way.rb

@@ -234,8 +234,8 @@ class Way < ActiveRecord::Base
 
   def preconditions_ok?(old_nodes = [])
     return false if self.nds.empty?
-    if self.nds.length > APP_CONFIG['max_number_of_way_nodes']
-      raise OSM::APITooManyWayNodesError.new(self.id, self.nds.length, APP_CONFIG['max_number_of_way_nodes'])
+    if self.nds.length > MAX_NUMBER_OF_WAY_NODES
+      raise OSM::APITooManyWayNodesError.new(self.id, self.nds.length, MAX_NUMBER_OF_WAY_NODES)
     end
 
     # check only the new nodes, for efficiency - old nodes having been checked last time and can't