Refactor script generation to make it fully on-demand

• Rename ShellScript to ShellConfiguration and remove all generated scripts
• Introduce ShellScriptType with different types of scripts
• Introduce GetConfiguration and GenerateScript for Shell interface
• Change ShellScript to Shell of Executor
• Remove GenerateScript from shells, instead provide a generic method with accepts ShellScriptType
• Introduce executeShellScript for Build, method which is responsible for generating and executing a shell script

@tmaczukin What do you think?