fix #73

I suppose the better way is to move weather adaptor to another open
weather engine despite the fact that OWM has provided me a special FOSS
permissions. I've changed weather provider to Yahoo! Weather because
there is no good way to provide my own API key to end-users except for
being compiled to the source code.

In other hand this solution leads to the fact that humidity and
atmosphere pressure is not available for forecast more. And moreover
pressure units has been changed for current weather.

+ fix possible memory leak in dataengine aggregator
+ add "special thanks" group to acknoledgment tab

sources/awesomewidgets/extweather.h

@@ -22,12 +22,10 @@
 
 #include "abstractextitem.h"
 
-#define OWM_URL                                                                \
-    "http://api.openweathermap.org/data/2.5/"                                  \
-    "weather?q=$CITY,$COUNTRY&units=metric"
-#define OWM_FORECAST_URL                                                       \
-    "http://api.openweathermap.org/data/2.5/"                                  \
-    "forecast?q=$CITY,$COUNTRY&units=metric"
+#define YAHOO_WEATHER_URL                                                      \
+    "https://query.yahooapis.com/v1/public/yql?format=json&q=select * from "   \
+    "weather.forecast where u='c' and woeid in (select woeid from "            \
+    "geo.places(1) where text='%1, %2')"
 
 
 namespace Ui
@@ -76,9 +74,8 @@ private:
     QNetworkAccessManager *manager;
     bool isRunning = false;
     Ui::ExtWeather *ui;
-    QVariantHash parseSingleJson(const QVariantMap json) const;
     void translate();
-    QString url(const bool isForecast = false) const;
+    QString url() const;
     // properties
     QString m_city = QString("London");
     QString m_country = QString("uk");