Add tasks module and rename trait files

src/app/states/skirmish_states/tasks/digging.rs

@@ -0,0 +1,6 @@
+use crate::app::widgets::CellWidget;
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct DiggingTask<'a> {
+    path: Vec<&'a CellWidget>,
+}