Support for segy ingestion of non-regularized data

[markspec]

Some types of segy data do not have a discrete integer bin on input. E.g. 2D CDP data might be regular in CDP and time but the offset dimension maybe represented by a floating point offset.

To handle cases like this the proposal is to have an ingestion header "index" which will just use a counter starting at 1and append traces to the "index" header.