Index file minor changes

- Minor changes in index.php file: keeping it clean and tidy, also
because of new installation process - added a check for installer
removal and empty config file in case if user abandoned installation
process at the very middle.
New installation process

- Reverted back to one-file installer, it was unnecessary to make it
modular o_O 99% of users and developers won't change there anything.
They actually need a working base to extend from, and old installer
simply did that nicely.

- Redo some code. Added HTML5 shiv for IE browsers and changed overall
installer style (YUI Pure CSS). Still, no images or anything using -
keeping it simple at installation process.