Impress App doesn't mess aound with styling of other Applications or the core.

I don't know the logic behind this, how Impress App's stylesheet affects the Calendar's layout and so of other application/core that use tables but changing from table to a class specific for Impress is solving it. 
Reference : https://github.com/owncloud/apps/issues/570 and https://github.com/owncloud/apps/issues/818
Please check @karlitschek @jancborchardt @arkascha @tanghus