Misc fixes for update checking

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

@@ -68,6 +68,8 @@ class MainActivity : AppCompatActivity(), NavigationBarView.OnItemSelectedListen
                 try {
                     UpdateChecker.check().collect(this@MainActivity::onAppUpdateAvailable)
                 } catch (_: CancellationException) {
+                } catch (e: AppUpdate.IgnoredException) {
+                    Timber.d(e)
                 } catch (e: Exception) {
                     Timber.w(e)
                     SmartSnackbar.make(e).show()

mobile/src/main/java/be/mygod/vpnhotspot/util/AppUpdate.kt

@@ -3,6 +3,8 @@ package be.mygod.vpnhotspot.util
 import android.app.Activity
 
 interface AppUpdate {
+    class IgnoredException(cause: Throwable?) : RuntimeException(cause)
+
     val downloaded: Boolean? get() = null
     val message: String? get() = null
     val stalenessDays: Int? get() = null