Objectbox-java: Support BigDecimal

[greenrobot]

Check https://stackoverflow.com/questions/46277927/how-can-i-use-objectbox-to-store-money-values-bigdecimal

As a first workaround we could provide an converter out of the box.

Open questions:

1. Can we have a efficient binary format - or should we just go with strings?
2. Can we make it sortable with reasonable effort?

[mvdh]

Any updates on this feature request?

[pandalion98]

Any updates?