Preferences / File Browser section made less confusing.

With T90317 the user did not find the filtering options within the File Browser itself. But he did find some setting for it in Preferences:

This section is confusing because it is not clear that these are defaults used for the next time the File Browser is launched. The user thought this would affect the display immediately. Further the awkward negatives make it worse, having to add a checkmark to turn on the hiding of something. And the mention of "dot files" does not generically apply to other operating systems, since this does not affect such files on Windows, just those with hidden file attributes.

This patch makes it look like the following:

It is clear that these are defaults and the items are less awkward.