[1.3.4 - 2.0.0] Backward compatibility fixes 

Changes in methods so that 2.0.0 is more backward compatible with 1.3.4

- Volt _compileSource is no more final
- getModelsManager is renamed getCollectionManager in Mvc/Collection class (changed in 1.3.3)
- fix #3048 bug with queryKeys in Xcache backend