Add support to allow emissions to start with a delay.

[NemesisMate]

Currently, when resetting the interval it starts from 0, meaning that if the particles are emitted each second it will wait to that first second the first time. There isn't a way to start immediately the emission but remain the interval.

Note: This should be added as an emitter option to the editor too.

[NemesisMate]

This PR proposes a fix.

[Aliaksandr Brui]

Implemented in the version 0.9.8