Changes to show hidden behavior:

Toggle in the View menu will always *initially* reflect what the preference
is, as before.

Changing the setting in the View menu will update the preference, as well
as all views in the current window.  Other open windows will not be affected.

Once those other open windows are closed, any new windows will of course
reflect the new state of the preference.

Removed show hidden toggle from preferences.
Add show hidden toggle to right-click menu
Change behavior of file properties window:

If hidden files set to shown, all files/dirs will be counted,
hidden or not.

If hidden files is NOT set to shown, the count will show:
x items (and y hidden items)

Size total will always include hidden files in calculation, regardless
of the current hidden preference.
Merge pull request #259 from mtwebster/toggle-hidden

Changes to show hidden files preference, calculations in file properties window