BAC-1199: Add logging of catchable fatals

The following information will be logged to ``datalog-s1:/var/log/private/exceptions.log``:

```
exceptions-WIKIA-WikiaDispatchedException: Internal Throw (Title::newFromText given an object)
exceptions-WIKIA-MWException: /wiki/Specjalna:Wersja   Exception from line 130 of /usr/wikia/source/app/includes/Title.php: Title::newFromText given an object
```

Additionally, ``X-MediaWiki-Exception: 1`` header will be added to the HTTP 500 response to ease debugging.

@Wikia/platform-team