3-dots menu for current breadcrumb item

[exalate-issue-sync]

Userstory

As a user who is in the folder "my Folder" I want to perform all context-menu actions on "my Folder" wihtout having to navigate back in the path hierarchy to do this.

(this is a nice-to-have story, because the story is already solved with "the sidebar opened and and nothing selected". Eliza suggested this feature long time ago, patrick mentioned that we used to have a community plugin for classic and i bring it up because having the contextmenu on the current breadcumb item feels really compfortable)

Acceptance Criteria

• Feature should be disabled for the "dropdown" breadcrumb on mobile
• "3-dots" icon at the end of the breadcrumb like on google drive
• opens context menu with all available actions (same as for the file row)

[pascalwengerter]

@JammingBen I've added a PoC PR in the design system, feel free to experiment with it via yarn link owncloud/owncloud-design-system#1786