Use custom type builders to define data types.

This eliminates the dependency on $wgDataTypes. We are
no longer using the data types defined per default in the DataType
module, but define our own instead, using WikibaseDataTypeBuilders.

This allows for complex validators to be set up, and allows the
injection of services into the validators. THis is however left
for later.

NOTE: this requires I38c8daa77 to be merged in the DataValues module.

Change-Id: Ie4d0aca547340a413872b32bb644171d151004ef
Merge "Use custom type builders to define data types."