text: Title: Headings semantics 
  Body: @nextcloud/designers I've noticed some issues with semantics that might be worth fixing - notably, headings. This might have to be separated into several issues/PRs:
  
  - [ ] `<h1>`  is used twice (it [shouldn't be](http://w3c.github.io/html/sections.html#rank)): once in the NC logo `<h1 class="hidden-visually">Nextcloud</h1>` and once in the `header-appname-container menutoggle` (app name). Possible solutions are changing the tag of the first one or removing the whole link from the Nextcloud logo (it's a weird link anyway, since it targets default app (Files), not Nextcloud itself)
  - [ ] because of the :arrow_up: , `<h1>` should never be used in apps - e.g. @nextcloud/news and @nextcloud/deck are breaking this "rule"
  - [ ] we have a default (core) style rules for `<h2>` and `<h3>`, but `<h4>` might be useful as well
  - [ ] `<h3>` should be used in right sidebar (I guess?) - in which case, we should come up with a good default rule for `#app-sidebar h3`; on a related note, should it actually be an input field, like in @nextcloud/calendar ?
  - [ ] default style for subtitle might be useful. @nextcloud/news has `.subtitle` which might be a good starting point (missing a more distinction for links IMO), @nextcloud/mail might apply something similar instead of the `.transparency`
  - [ ] the above mentioned apps could use `<header>` [tag](http://html5doctor.com/the-header-element/) to group title and subtitle
  
  Also possibly related to @nextcloud/theming 
  
  P.S. Sorry for bringing out such low-level issues :disappointed: 