Add ArcGISMapServer URL template support

[prushforth]

Implement a MapML proxy for existing ArcGIS MapServer interface services, and add the implementation of that proxy to https://github.com/Maps4HTML/MapMLServer/blob/master/src/main/java/org/mapml/MapMLPrinter.java#L206 as an alternate form of supported URL template i.e. ArcGISMapServerTemplate, useful for ArcGIS MapServer services, as opposed to tileUrlTemplates or wmsUrlTemplates as currently defined.

For example http://geoappext.nrcan.gc.ca/arcgis/rest/services/MMS/IMA_E/MapServer/export?bbox=-3256599.7214222914,1179536.074671093,3594226.7345222933,3743106.5513747153 is a MapServer service, there could be a URL template which supports creating an image element for MapML requests to such a service.