[QA] minor revision on cast operators
[DOC] Add documentation on new public routing function
Fix usage of default maps cache directory when it does not end in a separator.

Seems on Windows the preference 'maplayer_default_dir' does not end in a separator.

Thus when using the default value directly in downloading maps, the directory structure is not be created as expected.

Hence ensure for internal usage the cache_dir always ends with a separator.

This also fixes usage when the preferences is manually edited and the map default doesn't end in a separator.
Add a simple file properties dialog to show some details for a Viking file:

.the full filename path
.the modification time (useful to know when last saved)
.the file size