Make Message and Presence class final

In order to prevent users from trying to subclass those two, trying to
add their custom attributes (or attribute values) in the element of
those two, instead of using extension elements aka. PacketExtension.

See

- http://stackoverflow.com/q/26516386/
- http://stackoverflow.com/q/26507753/
- http://stackoverflow.com/q/26542601/
Remove unnecessary code in Message
Call pingServerIfNecessary in new thread

in order to prevent the BroadcastReceiver from timing out.

To prevent:

10-24 10:59:35.096 W/BroadcastQueue( 1044): Timeout of broadcast BroadcastRecord{43400df0 u0 org.igniterealtime.smackx.ping.ACTION} - receiver=android.os.BinderProxy@42d37cc0, started 60000ms ago
10-24 10:59:35.096 W/BroadcastQueue( 1044): Receiver during timeout: BroadcastFilter{42cee7b0 u0 ReceiverList{42cfd9f0 16003 org.projectmaxs.transport.xmpp/10149/u0 remote:42d37cc0}}

10-24 10:59:38.201 E/ActivityManager( 1044): ANR in org.projectmaxs.transport.xmpp
10-24 10:59:38.201 E/ActivityManager( 1044): PID: 16003
10-24 10:59:38.201 E/ActivityManager( 1044): Reason: Broadcast of Intent { act=org.igniterealtime.smackx.ping.ACTION flg=0x14 (has extras) }
10-24 10:59:38.201 E/ActivityManager( 1044): Load: 18.97 / 31.7 / 45.71
10-24 10:59:38.201 E/ActivityManager( 1044): CPU usage from 20588ms to 0ms ago:
10-24 10:59:38.201 E/ActivityManager( 1044):   0.4% 1044/system_server: 0.2% user + 0.1% kernel / faults: 188 minor 1 major
10-24 10:59:38.201 E/ActivityManager( 1044):   0.4% 9089/kworker/0:3: 0% user + 0.4% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0.1% 1567/mpdecision: 0% user + 0.1% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0.1% 28507/kworker/u:5: 0% user + 0.1% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 7/kworker/u:0H: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 148/mmcqd/0: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 14687/com.teslacoilsw.launcher: 0% user + 0% kernel / faults: 6 minor
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 3/ksoftirqd/0: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 1111/MC_Thread: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 1135/wpa_supplicant: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 1283/com.android.phone: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 11469/com.getpebble.android: 0% user + 0% kernel / faults: 1 minor
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 14971/com.google.android.apps.unveil: 0% user + 0% kernel / faults: 6 minor
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 28677/watch_server: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   0% 31539/kworker/0:2: 0% user + 0% kernel
10-24 10:59:38.201 E/ActivityManager( 1044): 1.2% TOTAL: 0.4% user + 0.5% kernel + 0.2% iowait
10-24 10:59:38.201 E/ActivityManager( 1044): CPU usage from 2536ms to 3060ms later:
10-24 10:59:38.201 E/ActivityManager( 1044):   9.2% 1044/system_server: 1.8% user + 7.4% kernel / faults: 56 minor
10-24 10:59:38.201 E/ActivityManager( 1044):     5.5% 1058/ActivityManager: 0% user + 5.5% kernel
10-24 10:59:38.201 E/ActivityManager( 1044):   1.3% 23415/kworker/0:1H: 0% user + 1.3% kernel
10-24 10:59:38.201 E/ActivityManager( 1044): 0% TOTAL: 0% user + 0% kernel + 0% iowait
10-24 10:59:38.208 I/ActivityManager( 1044): Killing 16003:org.projectmaxs.transport.xmpp/u0a149 (adj 0): background ANR
s/connection()/connection/ in PingManager