Enable updating the treeview to allow setting a blank waypoint symbol.
[QA] Function should have only local scope.
[QA] Add missing include as this header uses an externally defined type DownloadMapOptions.
Add Wikimedia Toolserver GeoHack as a webtool.

Stick it in the osm file for now.
Fix use of scaled tile image when tile image not present.

Due to the two stage initialization of the VIK_MAP_SOURCE the tilesize was actually set to zero.
This leads to the mapslayer redraw *not* trying differing tile zooms to get a pixbuf for the current zoom level.

First vik_map_source_init is performed (such as vik_slippy_map_source_init(),
 which sets a specific tilesize value in the first g_object_new() call.

However since the tilesize parameter is 'G_PARAM_CONSTRUCT | G_PARAM_READWRITE',
 on the second g_object_new() such as in osm_init(), since the tilesize is not specified
 it seems it is then 'constructed' with the default g_param value - which in this case is 0.

Thus to prevent the resetting of the tilesize, set it to 'G_PARAM_READWRITE'
and hence the extra (re)construction is avoided.

This has been broken since early 2010 in commit SHA1:0f08bd0dd39944f099a00af0ae8fe319d8bd9fa0
when the tilesizes at the osm.c level where removed, even though the underlying flaw is from earlier:
at least SHA1:31f3c5e7091825bd5c73f0d538741906cb4e4501