HistoryLimit: default to 0 (unlimited)

There does not seem to be any reason to set the default history to 30
days. By default, it is expected that communication programs keep
history forever, unless the user cleans them or sets a limit.

Change-Id: Ic860f61a8d4c372a9f7377b24d8edfc6081bc977
Reviewed-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>

src/preferences.cpp

@@ -139,7 +139,7 @@ static const char * const ALSA_DFT_CARD    = "0";          /** Default sound car
 
 Preferences::Preferences() :
     accountOrder_("")
-    , historyLimit_(30)
+    , historyLimit_(0)
     , historyMaxCalls_(20)
     , zoneToneChoice_(DFT_ZONE) // DFT_ZONE
     , registrationExpire_(180)