Schedule instantiation

When a rendering is active instantiation will not happen right away.
but it will be scheduled. Currently it is possible to instantiate
only an assembly and an object.

This commit fixes issue #327
Fixed bug when entering values lower than the min for sliders
Merge pull request #362 from vidarn/master

Fixed bug when entering values lower than the minimum for sliders
Schedule instantiation: coding style fixes

A few thinkg overlooked in the previous commit.
Merge pull request #360 from marius-avram/B327

Schedule instantiation