Reorganize project files into subfolders

- CGI scripts => cgi-bin folder
- CSS files	=> css folder
- images	=> assets folder

- Use relative paths throughout the whole project
- change permissions:
	- make eliza.py executable
	- make pc.jpg not executable
Explain in README how to run the code
Merge pull request #2 from sebroeder/master

Add missing subfolders and reorganize project files