SF#3028797: Remember last directory used when saving / opening main files.

By changing the working directory potentially allows opening files with relative paths to work.
Make more portable .vik file, as don't save the map cache directory if it's the map cache default directory.

The map cache default directory is dependent on the user and OS, however on reading in when it's blank it automatically puts in the map cache default directory.

Unlike the previous effort SHA1: 39aec6c6b87a324981a6e1d028ba345320a444ad
This uses the fixed value MAPS_CACHE_DIR rather than the preference value in case the preference has changed.
Add 'Advanced' preferences tab.
SF#2998555: Control of saving Absolute vs Relative Paths in .vik files

For any file name paths potentially save in relative (../../ etc...) style if specified by the preferences.

Affects:
. Waypoint images
. DEM file list
. Map directory cache
. GeoRef file image

A new level of 'Advanced' preferences tab has been created to store the controlling setting.
Reduce wasted space in the Preferences dialog if there are lots of tabs.

Switch to tabs being vertically listed on the left if there are 'a lot' of them.
[NB thus doesn't effect the TrackWaypoint layer properties layout]
SF#3608417: Add Preference option to control the display of the track creation distance tooltip.

Since the distance is also shown in the statusbar, one may consider the tooltip to get in the way.
Thus you can now turn it off.
SF#3387591: Improve keyboard copy+paste behaviour when the editing a layer name in the treeview.

Since the default keyboard shortcuts are overridden, we handle them even when a cell is being edited.
Ensure when editing that keyboard shortcuts do something more sensible then copy/pasting layer data.
Thus as we can't get to the internals of the text actually selected,
just copy and paste the layer name.

This also means we can accept pasting in plain text, which can be useful in naming layers.

Also ignore ctrl+<arrow> when editing the treeview which otherwise moves the viewport.
Add 'Creation' sort option for saving GPX tracks.

This will then save tracks in the order they were read in or created.
Really fix showing map timestamps on Windows on the map tile info dialog.

For some reason it would always show '(null)', so revert back to strftime() and use gmtime() too.
Ditch the gdate stuff as it doesn't simplify the code either
Fix a_vik_gpx_export_wpt_sym_name internal type