Made GPX notification E-Mails translatable

The multiline 'notifier.gpx_notification.success.loaded_successfully'
message is how one should properly do multiline messages to be
embedded into E-Mail. It wraps at 80 columns (if translated correctly)
and isn't as inhererently limited as splitting the E-Mail into one
message per-line like the other notification messages do it.

app/models/notifier.rb

@@ -33,7 +33,7 @@ class Notifier < ActionMailer::Base
 
   def gpx_success(trace, possible_points)
     common_headers trace.user
-    subject "[OpenStreetMap] GPX Import success"
+    subject I18n.t('notifier.gpx_notification.success.subject')
     body :trace_name => trace.name,
          :trace_points => trace.size,
          :trace_description => trace.description,
@@ -44,7 +44,7 @@ class Notifier < ActionMailer::Base
   def gpx_failure(trace, error)
     common_headers trace.user
     from "webmaster@openstreetmap.org"
-    subject "[OpenStreetMap] GPX Import failure"
+    subject I18n.t('notifier.gpx_notification.failure.subject')
     body :trace_name => trace.name,
          :trace_description => trace.description,
          :trace_tags => trace.tags,

app/views/notifier/_gpx_description.rhtml

@@ -1,14 +1,14 @@
-Hi,
+<%= t'notifier.gpx_notification.greeting' %>
 
-It looks like your GPX file
+<%= t'notifier.gpx_notification.your_gpx_file' %>
 
   <%= @trace_name %>
 
-with the description 
+<%= t'notifier.gpx_notification.with_description' %>
 
   <%= @trace_description %>
 <% if @trace_tags.length>0 %>
-and the following tags:
+<%= t'notifier.gpx_notification.and_the_tags' %>
 <% @trace_tags.each do |tag| %>
   <%= tag.tag.rstrip %><% end %><% else %>
-and no tags.<% end %>
+<%= t'notifier.gpx_notification.and_no_tags' %><% end %>

app/views/notifier/gpx_failure.rhtml

@@ -1,9 +1,9 @@
 <%= render :partial => "gpx_description" %>
-failed to import. Here's the error:
+<%= t'notifier.gpx_notification.failure.failed_to_import' %>
 
   <%= @error %>
 
-More information about GPX import failures and how to avoid
-them can be found at:
+<%= t'notifier.gpx_notification.failure.more_info_1' %>
+<%= t'notifier.gpx_notification.failure.more_info_2' %>
 
-  http://wiki.openstreetmap.org/wiki/GPX_Import_Failures
+  <%= t'notifier.gpx_notification.failure.import_failures_url' %>

app/views/notifier/gpx_success.rhtml

@@ -1,3 +1,2 @@
 <%= render :partial => "gpx_description" %>
-loaded successfully with <%= @trace_points %> out of a possible
-<%= @possible_points %> points.
+<%= t'notifier.gpx_notification.success.loaded_successfully', :trace_points => @trace_points, :possible_points => @possible_points %>