This commits series introduces bars which may be calculated from any
custom formula. For a start I've renamed $bar*tag to $bar* and add new
configuration parameters to graphical items.
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
