Implement way to export race data

[vyruz1986]

The web UI/websocket interface should allow to export history race data. Several options should be available to the user:

• Export all races in memory
• Export collection of races (from... to...)
• Export one specific race

For now it should be sufficient to export race data in JSON format.
Each export, regardless of number of races that will be exported, should be an array of racedata objects

It should be possible to specify in the security parameters whether the exporting of races is allowed for anonymous users or only to admin users