Recognise links in comments, etc.

Links that are entered in comments, activities, etc. should be recognised and rendered as links. The best way to do this might be as a TrimPath modifier, although I'm not sure if TrimPath modifiers can be chained.

Examples of TrimPath modifiers can be found in the oae.api.util.js file:

```
'encodeForHTML': function(str) {
  return security().encodeForHTML(str);
},
'encodeForHTMLAttribute': function(str) {
  return security().encodeForHTMLAttribute(str);
},
'encodeForURL': function(str) {
  return security().encodeForURL(str);
}
```