Seperate options for activating access counter and popular widget

[sb0001]

I'd suggest to make two options available:

1. option: activate counter for accessed pages
2. option: show popular widget (only available if above is active)

As an alternative the existing fields in configuration>widgets could be used like this:

1. Rename "Popular_posts_widget" to "Activate access counter"
2. If "Popular_posts_widget_at_most" equals 0 the widget itself will be hidden