Added a new class: DataStoreZabbix.

The purpose of this patch is to stub files and functions.
So nothing was added from a functional standpoint.

This patch is a part of (A) to (C) in the following figure.

<< Next milestone >>
showing a 'Overview' of ZABBIX PHP UI. The assumed design of
the data stream is the following.

[Zabbix Server] =>
  (A) ArmZabbAPI -> (B) DataStoreZabbix -> (C) VirtualDataStoreZabbix
    -> (D) SQLProcessorZabbix -> (D) FaceMySQLWorker  => ZABBIX PHP client