[Example] Remove layer before adding layer if layer is added in place source example

[Chaoba]

This PR adds a variable layerAdded to record the current status of imageLayer and will remove it before adding it, so that show Layer and show layer below water act normally.
Also removes the redundant Row widget.

Before	After
device-2021-11-16-144023.mp4	device-2021-11-16-143651.mp4

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[felix-ht]

LGTM

[felix-ht]

@tobrun do you have any idea why the build fails to get the token?

[tobrun]

@tobrun do you have any idea why the build fails to get the token?

probably because of moving the repo to the new organization..
Re-added them, even though they were still listed.
Let's try again

[tobrun]

@tobrun do you have any idea why the build fails to get the token?

After double checking this all, it seems to be related to not sharing env. secrets with forked pull requests (which isn't a configuration or smth like that..)

[felix-ht]

@tobrun GitHub actions are quite messy - so what's the policy we merge fork prs without the builds as long as the review approved it?

We could also run a post merge build so stuff would not break without someone noticing it.

[tobrun]

We could also run a post merge build so stuff would not break without someone noticing it.

Not ideal but for now that way of working is fine.