Share function/button for permalink/map context

[justb4]

Issue #38 will provide permalink functionality, i.e. being able to gather, provide and load a map-context (center+zoom or extent, rotation, layers,..) using URL location query/hash.

This issue is to provide the user with a "share" option, usually via a "Share Button". This function will interwork with the permalink-function (component/ol/PermalinkController class) of #38 . The following is foreseen:

• optional permalink button in header menu
• when clicked minimally a "copy" option for the share-URL, plus:
• option: "embed" to copy an iframe for embedding into a website
• option: "embed" a mailto to email the share-URL

The existing permalink "apply" (load) can be reused when a user accesses the app with a share-URL.

An example can be found here (open the tab "Teilen").