Add of About dialog in OpenFLUID-Builder with Qt

* Added "About" dialog
* Added texts for "About" dialog as builderconfig strings
* Added action for sending an email to OpenFLUID contact address
* Refactored HomeLabel class as ClickableLabel,
  apart from the HomeWidget class file
* Added resources for "About" dialog  
* Cleaned code  

(references OpenFLUID/openfluid#246)
Opening example projects in OpenFLUID-Builder with Qt

* Added dialog for selection of the example project to open
* Enabled action to reinstall provided example projects
* Adjusted design of "About" dialog
* Updated AUTHORS file
* Cleaned code  

(references OpenFLUID/openfluid#246)