This is a meta-task for a series of things we need to do in order not to accumulate further technical debt on the appservers.

In short, the following things need to be taken care of:

1. Upgrade libicu so that we can use the system-provided one
2. Drop all references to zend-specific configs in the mediawiki classes, wherever they're not needed
3. Make mediawiki classes compatible with Debian Jessie
4. Reduce the app layer clusters to appropriate sizes
5. Upgrade the appservers to jessie
6. Profile and improve the puppet execution time for the role::mediawiki::* classes