Missing "+" (Add) button in channels to add new tabs

[PatrickSchmiedeke]

Hello,

I am a little unsure if there a new permissions to add tabs to a channel. Same goes for the function to add new Apps to teams. 

with preview off:

there is a + button to add a new tab for excel files etc.

with preview on:

it is missing

Same with the App button

with preview off:

with preview on:

[#2]

App Button is now available but the '+' button to add new Tabs to channel is still missing.