[Enhancement] Allow "secret" toggle to be used from embeding journal pages

[Bradeck]

Constated behavior
The secret button to reveal / hide secret sections don't work when the secret block is in an embedded page.
It also don't give any message explaining why it doesn't work.

Steps to reproduce
1/ Create a journal page, create a secret block inside it
2/ Create another journal page, and embed the page created in step 1
3/ Try to toggle the secret block from the page created in step 2

Wished for behavior
Allow the button to work, even if the secret block is from an embeded journal page.

If it's not possible, show a notification / warning explaining that the reveal / hide action must be made on the embedded journal page.

[arbron]

Seems like this is more of a core issue, since the system doesn't handle embedding normal journal pages itself.