PHP mimetype stuff should also use config/mimetypealiases.json

Update version to 8.2 in README and bower

[config sample] Update info about appstore

Javascript to fetch mimetype icons

Fix regression of button at public download page

add recursive copy polyfill for storage backends

Switch to new javascript mimetype resolver

This makes it possible to retrieve the icon for mimetypes in javascript.
It makes no additional queries to the server to retrieve the mimetype.

* config/mimetypealiases.json added
* mimetype.js: this is where the logic resides to convert from mimetype
  to icon url
* mimetypelist.js: generated file with a list of mimetype mapping (aliases)
  and the list of icon files
* ./occ maintenance:mimetypesjs : new command for occ to gernerate
  mimetypes.js
* unit tests updated and still work
* javascript tests added
* theming support
* folder of the theme is now present in javascript (OC.theme.folder)

Replace readonly wrapper with permissions mask

add occ tool to delete versions

* introduced with #17159

Reorganize sampe.config.php

Check if response could get generated

Improve federated cloud sharing activities

Add OCS API to send, get, accept and decline remote shares

Add occ app:list and ldap:show-config to issue_template.md

Kill more legacy classes