Add page context to template filter, resolves #1603 (#1818)

* Add a test for template filter
* Add a test for template filter with page parameter
* Passing page as a parameter to template filter

lib/gollum.rb

@@ -29,9 +29,10 @@ module Gollum
       @@filters[pattern] = replacement
     end
 
-    def self.apply_filters(data)
+    def self.apply_filters(wiki_page, data)
       @@filters.each do |pattern, replacement|
-        data.gsub!(pattern, replacement.call)
+        params = replacement.parameters.length == 0 ? nil : wiki_page
+        data.gsub!(pattern, replacement.call(*params))
       end
       data
     end

lib/gollum/app.rb

@@ -369,7 +369,7 @@ module Precious
         @name = wikip.name
         @ext  = wikip.ext
         @path = wikip.path
-        @template_page = load_template(@path) if settings.wiki_options[:template_page]
+        @template_page = load_template(wikip, @path) if settings.wiki_options[:template_page]
         @allow_uploads = wikip.wiki.allow_uploads
         @upload_dest   = find_upload_dest(wikip.fullpath)
 
@@ -661,9 +661,9 @@ module Precious
       end
     end
 
-    def load_template(path)
+    def load_template(wiki_page, path)
       template_page = wiki_page(::File.join(path, '_Template')).page || wiki_page('/_Template').page
-      template_page ? Gollum::TemplateFilter.apply_filters(template_page.text_data) : nil
+      template_page ? Gollum::TemplateFilter.apply_filters(wiki_page, template_page.text_data) : nil
     end
 
     def update_wiki_page(wiki, page, content, commit, name = nil, format = nil)