Update ical4android and vcard4android; add HTTP/2 ping every 45 secs to avoid cancellation

        /** [OkHttpClient] singleton to build all clients from */

        val sharedClient: OkHttpClient = OkHttpClient.Builder()

                // set timeouts

                // Set timeouts. According to [AbstractThreadedSyncAdapter], when there is no network

                // traffic within a minute, a sync will be cancelled.

                .connectTimeout(15, TimeUnit.SECONDS)

                .writeTimeout(30, TimeUnit.SECONDS)

                .readTimeout(120, TimeUnit.SECONDS)

                .pingInterval(45, TimeUnit.SECONDS)     // avoid cancellation because of missing traffic; only works for HTTP/2

                // keep TLS 1.0 and 1.1 for now; remove when major browsers have dropped it (probably 2020)

                .connectionSpecs(listOf(

Subproject commit 535e04e7acfe6be78b77c9895fc07b333be5a477

Subproject commit 7d3045f3b30fffb65eb9b6535af065d21c57a70d

Subproject commit ec994f5470dab937c958c5cea13e9c58cef366bb

Subproject commit d4e00ff429ea8e89ce27232f6fd225ca76d63242