Depth in/decrease used as equivalent to outline in/out

[Jean-Marc Lasgouttes]

Hello,

I am looking for feedback about
https://www.lyx.org/trac/ticket/12417

Basically, now Tab and the depth icons invoke outline in/out when on a 
sectioning layout.

Do you find that this is confusing? The fact is that these two bindings 
have different behavior on layouts that follow the current one. Outline 
stuff is more global (and somewhat broken, see #9375).

The ticket asks to revert b08791f7 (icons) and 31398779/9ab9f2b1 (Tab 
key). What are your thought about this functionality?

JMarc