Bug #746: Error is we extend the timeline to the borders of the parent

Fix for https://github.com/alterm4nn/ChronoZoom/issues/746

Problem: Server only supports 8 decimals which is down to seconds-precision. However, client sends sub-second precision.

Fix: Reuse client constant (allowedMathImprecision) to round decimals to 7 decimals which the server currently supports. This could enable minute-precision timelines at some point.