Honor "safe for web app" flags for import/export handlers

tailbone/templates/importing/runjob.mako

@@ -44,7 +44,12 @@
     </once-button>
     <b-button type="is-primary"
               @click="submitRun()"
+              % if handler.safe_for_web_app:
               :disabled="submittingRun"
+              % else:
+              disabled
+              title="Handler is not (yet) safe to run with this tool"
+              % endif
               icon-pack="fas"
               icon-left="arrow-circle-right">
       {{ submittingRun ? "Working, please wait..." : "Run this ${handler.direction.capitalize()}" }}

tailbone/views/importing.py

@@ -129,6 +129,7 @@ class ImportingView(MasterView):
             'handler_spec': handler.get_spec(),
             'direction': handler.direction,
             'direction_display': handler.direction.capitalize(),
+            'safe_for_web_app': handler.safe_for_web_app,
         }
 
         if keep_handler:
@@ -314,7 +315,13 @@ class ImportingView(MasterView):
 
         if self.request.POST.get('runjob') == 'true':
 
-            # will invoke handler to run job
+            # will invoke handler to run job..
+
+            # ..but only if it is safe to do so
+            if not handler.safe_for_web_app:
+                self.request.session.flash("Handler is not (yet) safe to run "
+                                           "with this tool", 'error')
+                return self.redirect(self.request.current_route_url())
 
             # TODO: this socket progress business was lifted from
             # tailbone.views.batch.core:BatchMasterView.handler_action