[[ Bug 20217 ]] Indicate layerMode issues when setting

[montegoulding]

This patch adds a layerMode setter command so that the effective layermode can be checked after setting to ensure the user is informed if it differs from the setting they applied.

[montegoulding]

@runrevmark @livecodeali I have left this as WIP mainly because for some reason getting the effective layerMode directly after setting the layerMode returns the previous value. There must be some refresh point or something. I tried adding a wait and that didn't work. The general idea is to let users know exactly what's blocking their setting.