Add GUI support for downloading planner data.

Including HTML and PDF formats, which constitutes the lookahead report.

lib/www/client/source/src/views/Plan.vue

@@ -4,6 +4,40 @@
       <v-card-title>
         <v-toolbar flat>
           <v-toolbar-title>Plan</v-toolbar-title>
+          
+          <v-menu v-if="items">
+            <template v-slot:activator="{on, attrs}">
+              <v-btn class="ml-5" small v-on="on" v-bind="attrs">
+                <span class="d-none d-lg-inline">Download as…</span>
+                <v-icon right small>mdi-cloud-download</v-icon>
+              </v-btn>
+            </template>
+            
+            <v-list>
+              <v-list-item
+                :href="`/api/project/${$route.params.project}/plan/?mime=text%2Fcsv&download`"
+                title="Download as a comma-separated values file."
+                disabled
+              >CSV</v-list-item>
+              <v-list-item
+                :href="`/api/project/${$route.params.project}/plan/?mime=application%2Fgeo%2Bjson&download`"
+                title="Download as a QGIS-compatible GeoJSON file"
+              >GeoJSON</v-list-item>
+              <v-list-item
+                :href="`/api/project/${$route.params.project}/plan/?mime=application%2Fjson&download`"
+                title="Download as a generic JSON file"
+              >JSON</v-list-item>
+              <v-list-item
+                :href="`/api/project/${$route.params.project}/plan/?mime=text%2Fhtml&download`"
+                title="Download as an HTML formatted file"
+              >HTML</v-list-item>
+              <v-list-item
+                :href="`/api/project/${$route.params.project}/plan/?mime=application%2Fpdf&download`"
+                title="Download as a Portable Document File"
+              >PDF</v-list-item>
+            </v-list>
+          </v-menu>
+          
           <v-spacer></v-spacer>
           <v-text-field
             v-model="filter"