Implement partial reordering or habit groups

uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/list/views/HabitCardListController.kt

@@ -50,12 +50,20 @@ class HabitCardListController @Inject constructor(
         if (from == to) return
         cancelSelection()
 
-        val habitFrom = adapter.getItem(from)
-        val habitTo = adapter.getItem(to)
-        if (habitFrom == null || habitTo == null) return
-
+        val habitFrom = adapter.getHabit(from)
+        val habitTo = adapter.getHabit(to)
+        if (habitFrom != null && habitTo != null) {
             adapter.performReorder(from, to)
             behavior.onReorderHabit(habitFrom, habitTo)
+            return
+        }
+
+        val hgrFrom = adapter.getHabitGroup(from)
+        val hgrTo = adapter.getHabitGroup(to)
+        if (hgrFrom != null && hgrTo != null) {
+            adapter.performReorder(from, to)
+            behavior.onReorderHabitGroup(hgrFrom, hgrTo)
+        }
     }
 
     override fun onItemClick(position: Int) {

uhabits-core/src/jvmMain/java/org/isoron/uhabits/core/ui/screens/habits/list/ListHabitsBehavior.kt

@@ -118,6 +118,10 @@ open class ListHabitsBehavior @Inject constructor(
         }
     }
 
+    fun onReorderHabitGroup(from: HabitGroup, to: HabitGroup) {
+        taskRunner.execute { habitGroupList.reorder(from, to) }
+    }
+
     fun onRepairDB() {
         taskRunner.execute {
             habitList.repair()