Add capability to save layer defaults from outside the layer defaults code.
Enable Map Cache layout control per map.

The default for new users is the standard OSM layout that should be compatible with other tools.

For existing users the legacy method is kept as the default.

Users can change the default used via the layer defaults configuration or on a map by map basis in their .vik files.

A python script tool (run manually) is provided to assist migrating cache from one format to another (see later commits).
Default map caches for new users to use the OSM layout scheme.
Add map name property which is used in the directory path of the cache storage.

If map name is not specified then fallback to the label name.
[QA] Rename mode to id.
Enable importing from an mbtiles file to Viking cache via the python tool.
Rename viking cache tool in preparation for more than just mbtiles usage.
Python 3 compatibility.
More reliable file processing in creating an mbtiles file.

Only attempt to use file names that are composed of digits.
Change tool to require specifying the mode of operation.
Enable Cache conversion in the Python tool viking-cache.py

Includes method to move an existing cache from the legacy format to the more standard OSM layout.
For simplicity it uses an id to fixed name rather than trying to parse any maps.xml.
Add and use capability of defined individual map types zoom minimum and maximum levels.

Various tile servers have differing zoom extents.
Thus don't need to generate download requests that we know are going to fail.
The zoom levels can be customized for new maps.

NB this only caters for zoom levels that don't vary across the world.
It is possible some tile servers support differing zoom levels in different regions.
[WINDOWS] Add cache tool script into Windows distribution build.
Improve tile info dialog message to print out the filename even when cache file is not on disk.
SF Features#121: Support reading alternative forms of tile image names.

Ability to specify the file name extension of tiles read from the disk cache.
The property is 'file-extension' in the maps.xml configuration file.
[QA] Explain some more map configuration options.
Read OSM Metatile capability and basic test with single example metatile.

Based on https://github.com/openstreetmap/mod_tile/
Version 0.4
Add OSM Metatiles as a Map Type so one can read metatiles directly from disk.

e.g. as generated by renderd/mod_tile or tirex.
[DOC] Remove references to defunct Terraserver maps.
[DOC] Improve Map Layer documentation including properties of the map layer.