sending load message to the embed control should reset the snapshot list

[mscherotter]

Snapshots don't work if the data set is different, so when the snapshot list is not reset when a new data set and insight is loaded, the snapshots fail to load correctly.
Recommend resetting snapshots when load message is received and data changes.

[danmarshall]

Snapshots can refer to DataFile objects via url, such that a list of snapshots can load the dataset to which it is bound. Perhaps we should add a flag to the load command to clear the snapshots.