[MlMt] add ESC to close a child message view

[Michael Nietzold]

When:

- I have the eMails in a list
- when I hit enter it opens a message in a single view as a new child 
view

When I do:
- to close I need to click on the red x or hit CMF+w

What I expect:
- somehow (because I always hitting it) I expect that i can close it 
just with the ESC key

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