[feature/add-demo-account] Add Account: Provide Demo Account Setup

[hosy]

Description

Added a new item Demo Account to the Add Account action which provides a preconfigured setup for the ownCloud demo server.
This item is only visible, if the server list is empty.
The branded login view will be used to add the demo account, which provides also further information for ownCloud and can be configured via the Branded.plist
On iOS 14 the new UIMenu will be used, on iOS 13 UIAlertViewController will be used instead to present the account items.

Related Issue

#512

Motivation and Context

There are also users, which are interested in ownCloud and which wants to test the ownCloud iOS app, but without having an own ownCloud instance.

How Has This Been Tested?

• Tap on Add account, if the server list is empty
• Select Demo Account
• Follow the setup instructions
• If a bookmarks was configured, the action Demo Account should no longer appear

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[mneuwert]

@hosy is menu support not available on iOS13?

[hosy]

Not for UIBarButtonItem and UIButton only for contextual menus

[mneuwert]

@hosy @michaelstingl @jesmrec
Just as an idea: instead of always requiring two taps to create an account be could have a second button on this screen "Check out Demo" or something like that which directly would add and open demo account