Built the QCubed installer

Hello everyone, 

Just finished with the QCubed installer so that a newbie could start off with the framework easily. Please test it and let me know. The changes, in words are:

* The default index page points to the installer index page which allows you to make a choice between the installer or the old start page (actually the config checker we already have).
* The Installer is divided in 3 steps:
    1. Asks the installation directory - makes a guess based on $_SERVER['DOCUMENT_ROOT']; and current file location.
    2. Verifies the sent strings, fills the input fields with defaults. The fields are for ```__DOCROOT__```, ```__VIRTUAL_DIRECTORY__``` and ```__SUBDIRECTORY__``` and database settings. THe user can enter the values and click on 'Write configuration' button to go to the final step.
    3. This file reads in the sample configuration file (Configuration.inc.php.sample) and replaces the values submitted by user. I have modified the sample config file to make the process easy. 
* If the installer sees that a configuration file is already present, then it does not overwrite the file but still presents entire text in case the user wants to overwrite (has to be done manually). 

This is to make sure that an accidental click does not ruin all the previous settings. 

Please test and let me know of any improvements. The styling is very simple as of now. 

Regards,
Vaibhav