added option to clean message history

app/src/main/java/com/geeksville/mesh/MainActivity.kt

@@ -846,6 +846,10 @@ class MainActivity : AppCompatActivity(), Logging,
                 Toast.makeText(this, item.title, Toast.LENGTH_SHORT).show()
                 return true
             }
+            R.id.clear_history -> {
+                model.messagesState.cleanMessages()
+                return true
+            }
             else -> super.onOptionsItemSelected(item)
         }
     }

app/src/main/java/com/geeksville/mesh/model/MessagesState.kt

@@ -41,6 +41,12 @@ class MessagesState(private val ui: UIViewModel) : Logging {
             messages.value!! + m
     }
 
+    /// clean messages from our UI
+    fun cleanMessages() {
+        debug("cleaning messages")
+        messages.value = emptyList()
+    }
+
     fun updateStatus(id: Int, status: MessageStatus) {
         // Super inefficent but this is rare
         debug("Handling message status change $id: $status")

app/src/main/res/menu/menu_main.xml

@@ -7,6 +7,10 @@
         android:tint="#FFFFFF"
         android:title="@string/disconnected"
         app:showAsAction="ifRoom" />
+    <item
+        android:id="@+id/clear_history"
+        android:title="Clear History"
+        app:showAsAction="withText" />
     <item
         android:id="@+id/about"
         android:title="@string/about"