Fixes for reticle preview and `allowReticleChange`

[bboudaoud-nv]

This branch fixes a buggy interaction between specifying reticle configuration parameters at the experiment/session/trial level and using allowReticleChange = true to enable the user menu reticle configuration GUI.

The app now treats specifying any reticle configuration at the experiment/session/trial level as equivalent to setting the corresponding field's allowReticle[X]Change parameter to false. Thus the only reticle parameters users are free to configure are those not specified as part of experiment configuration.

Merging this PR closes #361

[bboudaoud-nv]

A fuller list of changes in this branch include:

• Automatically update the user menu at the beginning of each trial
• Update the reticle preview (to what is actually drawn) on any change to reticle parameters (not just index)
• Implement a ReticleConfig != operator to support the item above
• Conditionally show user menu reticle options based on what is specified in the experiment config
• Fix a bug keeping reticle change time from showing when color change was disabled