Handle multiple search params in the imagery_url

[willemarcel]

In the example we have on the Readme file, the imagery_url has only one search param (blankTile=false):

http://devseed.com/ds-annotate?classes=farm,00FFFF%7Ctree,FF00FF&name=Farms-mapping&imagery_type=tms&imagery_url=https://gis.apfo.usda.gov/arcgis/rest/services/NAIP/USDA_CONUS_PRIME/ImageServer/tile/%7Bz%7D/%7By%7D/%7Bx%7D?blankTile=false&project_bbox=-90.319317,38.482965,-90.247220,38.507418

We need to handle correctly urls with multiple search params, like imagery_url=https://gis.apfo.usda.gov/arcgis/rest/services/NAIP/USDA_CONUS_PRIME/ImageServer/tile/%7Bz%7D/%7By%7D/%7Bx%7D?blankTile=false&apikey=12345.