* increased main priority to the half of maximum priority
* introduced define for minimum stack size
* decreased stack size for uart0 thread
* merged commands for rtc shell module to one command (date)
* cleanup of header includes
* added drivers directory to doxygen file
* added missing include to sht11 header
* added rtc and sht11 support to default project
* added rtc to auto_init
* added rtc and sht11 support to shell