Add file names to context output in HTML report

in partial completion of #39

lib/brakeman/format/style.css

@@ -60,6 +60,11 @@ p {
    background-color: white;
  }
 
+ table caption {
+   background-color: #FFE;
+   padding: 2px;
+ }
+
  table.context {
    margin-top: 5px;
    margin-bottom: 5px;

lib/brakeman/report.rb

@@ -528,7 +528,8 @@ class Brakeman::Report
     else
       CGI.escapeHTML(message)
     end <<
-    "<table id='#{code_id}' class='context' style='display:none'>"
+    "<table id='#{code_id}' class='context' style='display:none'>" <<
+    "<caption>#{(warning.file || '').gsub(tracker.options[:app_path], "")}</caption>"
 
     unless context.empty?
       if warning.line - 1 == 1 or warning.line + 1 == 1