Add option to start repeater on boot

Fix #9.

mobile/src/main/java/be/mygod/vpnhotspot/BootReceiver.kt

@@ -0,0 +1,32 @@
+package be.mygod.vpnhotspot
+
+import android.content.BroadcastReceiver
+import android.content.ComponentName
+import android.content.Context
+import android.content.Intent
+import android.content.pm.PackageManager
+import androidx.core.content.ContextCompat
+import be.mygod.vpnhotspot.App.Companion.app
+
+class BootReceiver : BroadcastReceiver() {
+    companion object {
+        private val componentName by lazy { ComponentName(app, BootReceiver::class.java) }
+        var enabled: Boolean
+            get() = app.packageManager.getComponentEnabledSetting(componentName) ==
+                    PackageManager.COMPONENT_ENABLED_STATE_ENABLED
+            set(value) = app.packageManager.setComponentEnabledSetting(componentName,
+                    if (value) PackageManager.COMPONENT_ENABLED_STATE_ENABLED
+                    else PackageManager.COMPONENT_ENABLED_STATE_DISABLED, PackageManager.DONT_KILL_APP)
+
+        private var started = false
+    }
+
+    override fun onReceive(context: Context, intent: Intent) {
+        if (started) return
+        when (intent.action) {
+            Intent.ACTION_BOOT_COMPLETED, Intent.ACTION_LOCKED_BOOT_COMPLETED -> started = true
+            else -> return
+        }
+        ContextCompat.startForegroundService(context, Intent(context, RepeaterService::class.java))
+    }
+}