removed unused Po_Parser library
removed backup file
moved HTMLPurifier's cache out of the library into a new /tmp directory
use Composer to fetch and load vendor libraries

This patch adds proper Composer usage, in which all the vendor/ libraries are now removed
from this repository and are fetched after cloning/pulling it. This also makes us use the
Composer-generated autoloader, so I removed a lot of manual class-loads.

To clean this up even further, we let Composer always-include the global functions (the
cost of that is virtually zero, but it frees us from having to keep track of what file to include
for what function). This killed a good chunk of other require statements.

JSMin is not maintained anymore, so we should switch to something better soon. CSSMin
is also not Composer-ready, hence the two manual package declarations.

The psr-0 loading for Slim is there because this old (but last 1.x) version of Slim has an error
in its own composer.json, which makes it unloadable.
noticed this missing handler while testing the API for Composer stuff
rebuilt Propel files and added helper for Windows systems

Using Propel 1 with Composer is a nightmare on Windows:
https://github.com/propelorm/Propel/pull/588

The small batch file works around Propel by simply directly
invoking Phing.
fixed typo
Merge branch 'composer' of https://github.com/webvariants/datawrapper into webvariants-composer
Merge branch 'webvariants-composer' into develop

s merge is necessary,