Support projectDir that contains spaces

[ArsenyYankovsky]

Using command as following:

command "java - jar \"/my/path that/contains/spaces.jar\""

Will fail since we do:

def builder = new ProcessBuilder(command.split(' '))

[eskatos]

More generally, the tasks should provide a way to specify the command line elements by elements and take care of escaping/quoting, delegating that job to ProcessBuilder.