Add a confirmation dialogue when deleting activites..

..which have >0 facts.

Re #2

hamstertools/app.tcss

@@ -18,7 +18,7 @@ DataTable:focus .datatable--cursor {
     width: 50%;
 }
 
-ActivityEditScreen, ActivityMappingScreen {
+ActivityEditScreen, ActivityMappingScreen, ActivityDeleteConfirmScreen {
     align: center middle;
 }
 
@@ -62,3 +62,25 @@ ActivityMappingScreen AutoComplete {
 ActivityEditScreen Input {
     width: 60;
 }
+
+#dialog {
+    grid-size: 2;
+    grid-gutter: 1 2;
+    grid-rows: 1fr 3;
+    padding: 0 1;
+    width: 60;
+    height: 11;
+    border: thick $background 80%;
+    background: $surface;
+}
+
+#question {
+    column-span: 2;
+    height: 1fr;
+    width: 1fr;
+    content-align: center middle;
+}
+
+Button {
+    width: 100%;
+}