changed file structure, improved install script

renamed 'bin' to 'sgcheck-bin', because when having been installed the filename 'bin' would not be unique
the sgcheck command works now. Uses a global environmental variable to find out the location of the scripts to call.

the install script writes necessary commands into $HOME/.bashrc:
	SG_SCRIPT_PATH= ...
	export SG_SCRIPT_PATH
the 'export ...' is necessary, so that the variable is defined inside scripts when they are being executed.