Add sleep tracking, statistics module and backup features

Features:
- Sleep tracking with timer and manual duration input
- Statistics module with 5 tabs (daily summary, feeding, diapers, sleep, growth)
- Export/Import backup functionality in settings
- Complete German, French and Italian translations

app/src/main/java/it/danieleverducci/lunatracker/entities/LunaEvent.kt

@@ -30,6 +30,7 @@ class LunaEvent: Comparable<LunaEvent> {
         const val TYPE_FOOD = "FOOD"
         const val TYPE_PUKE = "PUKE"
         const val TYPE_BATH = "BATH"
+        const val TYPE_SLEEP = "SLEEP"
     }
 
     private val jo: JSONObject
@@ -100,6 +101,7 @@ class LunaEvent: Comparable<LunaEvent> {
                 TYPE_FOOD -> R.string.event_food_type
                 TYPE_PUKE -> R.string.event_puke_type
                 TYPE_BATH -> R.string.event_bath_type
+                TYPE_SLEEP -> R.string.event_sleep_type
                 else -> R.string.event_unknown_type
             }
         )
@@ -123,6 +125,7 @@ class LunaEvent: Comparable<LunaEvent> {
                 TYPE_FOOD -> R.string.event_food_desc
                 TYPE_PUKE -> R.string.event_puke_desc
                 TYPE_BATH -> R.string.event_bath_desc
+                TYPE_SLEEP -> R.string.event_sleep_desc
                 else -> R.string.event_unknown_desc
             }
         )