added art/splashscreen.*
added splashscreen.png to the resources
splashscreen displayed
added two constants : (compilation)ALLOW_SPLASHSCREEN and fixedparameters::splashscreen_maximal_duration
modified DipylonUI::go() so that the splashscreen is displayed only if the program is launched for the first time; added to settings the 'application/firstlaunch' keyword
added a new setting named 'application/displaysplashscreen' : the splash screen is only displayed if this setting is set to true
modified DipylonUI::go() : added a message on the splash screen
modified dipylonui.cpp : fixed minor glitches thanks to cpplint.py
Merge branch 'feature25' into dev
added ressources/images/splashscreen.*