Map information tool: Information about the map properties

[dl3sdo]

The map information tool informs about the number of map objects, templates and undo-/redo-steps. It informs about the number and names of map parts, symbols, colors, and fonts. It shows for each color the symbol(s) using the color. For each symbol in use the tools shows the used color(s) and the number of related objects.

[dl3sdo]

Any proposals for additional features?

[dg0yt]

For consistent naming, this should probably come as class MapInformationDialog, in map_information_dialog files.

[dl3sdo]

The PR needs to be adapted due to changes in #2158, thus the merge of #2158 shall be done first.