Enhancement: Improved accessibility of information and relationships

Headings have been added to the following views: Share, Edit/Create Share Link, Standard Toolbar and Manage Accounts.
The filename input field and the two switches are now linked to their labels.
The 'contentDescription' attributes of the buttons in the Edit/Create Share Link view have also been updated.

https://github.com/owncloud/android/issues/4362
https://github.com/owncloud/android/issues/4363
https://github.com/owncloud/android/issues/4371
https://github.com/owncloud/android/pull/4448
