Fixed referencing error to FatFreeCRM::Version and rss/atom link exceptions on dashboard


On the latest ffcrm master branch:

Bug 1:

To replicate:
1. In your logged in state in the dashboard, click on the "RSS" link at the bottom of the page.
2. You should see a:

    uninitialized constant FatFreeCRM::Version exception.

3. Similarly, this occurs when clicking on the "ATOM" link.

Bug 2:

After the bug fix on Bug 1:

1. Click on the "RSS" link at the bottom of the dashboard page again.
2. You should see a:

```ruby
    undefined method `full_name' for nil:NilClass

   10     @activities.each do |activity|
   11       xml.item do
   12         xml.author      activity.user.full_name
   13         # xml.guid        activity.id
   14         # xml.link        nil
   15         xml.pubDate     activity.created_at.to_s(:rfc822)
   16         xml.title       activity_title(activity)
   17       end
```

3. A similar error occurs when clicking on the "ATOM" link.

This is likely due to the RSS/ATOM view picking up activities that does not have a paper_trail 'whodunnit' attribute set. An example is when an activity is created when a user logs in and the system modifies the login_count.

An example of an activity that caused the original breakage of the above bugs:

```bash
=> #<Version id: 17, item_type: User, item_id: 1, event: update, whodunnit: nil, object: --- nusername: davidcnemail: zhchua@gmail.comnfirst..., created_at: 2013-06-30 04:09:27, object_changes: --- !map:ActiveSupport::HashWithIndifferentAccess n..., related_id: nil, related_type: nil>
```

This pull request attempts to fix the uninitalized constant exception by pointing to the correct constant "FatFreeCRM::VERSION::STRING" and the full_name breakage by changing to ensure that there's a user in the first place. 

On a functional point, there is also no reason to display user login changes in rss/atom feeds.