add custom name support for osm maps and terrain

[fredmarkus]

This PR adds the ability to provide custom names for terrain and osm map names. I have the following piece of code where I access map osm buildings and terrain data.

bpy.data.objects[f'Terrain.{str(index).zfill(3)}'].select_set(True)
bpy.data.objects[f'map_{index+1}.osm_buildings'].select_set(True)

I have parallelized this to download and access multiple different objects at the same time. My problem is now that the current implementation assigns an index to the name of the terrain and the osm map and when downloading in parallel, multiple maps end up with the same name. With this PR I can run:

bpy.context.scene.blosm.customName = f'{index+1}'
bpy.context.scene.blosm.terrainName = f'Terrain.{str(index).zfill(3)}'

which allows me to set custom names for each map that is downloaded.
@vvoovv Using these modifications with the code above in Python works fine; however, when i try to run this in the GUI in Blender I get an error saying: AttributeError: type object 'Renderer' has no attribute 'toJoin' I am not really sure why this is. Do you have an idea? I have marked the PR as a draft for now because of this.

Note: I have only tested this on the base version of blosm so I don't know how it would perform on the premium version.