Added composer.json and dependency on Slim
Improved error presentation for xdebug users.

- Also commented out some echos early in index.php
Changed expected headers to uppercase.
Switch to use composer installed Slim
Switch to use Slim installed via composer.

- Added composer.json and Slim dependency.
- Improved error reporting for xdebug users.
- Changed auth headers to uppercase convention.
Remove hard coded path 'api' and simplify includes.

- Introduce constants for the root paths.
- Get root paths using realpath.
Several Bug Fixes and Additions Thanks to Cambell Prince
Merge branch 'cambell-prince-master-cp'
Bug Fix inventory.inc function: inventory_locations_all()