BigInt/Datatypes enhancements

**Value omittion of autoincremental numerics**
For a integer column with autoincrement the value can be omitted while supplying values for other columns.

However that only worked for integers, not for bigints and so you were getting error:
`error: null value in column "id" violates not-null constraint`

It should be fixed and a test was added to cover this case.

**Enable the override of a datatype for autogenerated relation keys**
By default autogenerated keys for relations have Integer datatype. Allowing BigInts will further increase the range of data.