SyncCache: Fixed set_request method

OverflowError: Unsupported UTF-8 sequence length when encoding string
Change the worker ping api method to use MySQL replace (Fix #85)
Fixing TestSitemapFacter
Facters: Setting initial categories (Fix #74)
Represent a violation with details, if possible (re heynemann/holmes-web#25)

This commit add a new class, MaterialConveyor. It works like a
proper conveyor that process information before delivering it to
MaterialGirl.