All zomes which expose functions for bridging from other applications MUST also define a bridgeGenesis function (i.e. the "Bridge-To" side). Zomes which want to call functions in other applications MAY define a bridgeGenesis function and declare that they do so by setting the Zome.BridgeTo value in their DNA.
This function will be called just once when bridging is established. This allows applications to do any initialization which might be required for the bridging to operate. For example the holodex indexing mixin zome registers the node as an indexing node in the bridgeGenesis function.
side will be an integer indicating if this is a "from" or a "to" call. The constants HC.Bridge.From and HC.Bridge.To are defined with the appropriate integer values.
dna will be the hash of the dna on the other side of the bridge.
appData will be user specified data provided at bridge time. This function must return true if it is to succeed, and the bridge to form successfully.