#1643 Add support for EpochTimestamp and Decimal

[stonesmi]

Added support for two new column types in the Vuu backend. Further work will be required on the Front-end to support these.

1) EpochTimestamp

This is a wrapper around a Long, containing the number of Nanoseconds since Unix epoch. It uses less memory than java.time.Instant.

2) Decimal

This is a wrapper around a Long, containing a Decimal value that has been multiplied by 10^8 to move the decimal point. Any precision beyond 8 decimal places is lost. It also only supports Decimal values between -92,233,720,368.54775808 and 92,233,720,368.54775807

3) Misc

I also fixed a few issues that were spotted in the code as I added these features:

• Fixed a bug whereby unknown types aren't serialised, causing an incomplete array to be sent to the UI

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