feat(iOS): Integrate Auto Layout to render UI

[flexaddicted]

Platforms affected

iOS

Motivation and Context

The changes proposed through this PR have been introduced to make easier the management of the User Interface through Auto Layout. In fact, Auto Layout is now the de facto standard to handle layout in iOS.
Additionally the creation of the components has been refactored in order to identify clearly them within the code.

Description

These are the changes in detail:

• Replace frame based layout with Auto Layout.
• Create separate methods used to create all the elements of the user interface.
• Add an additional property, called extendwebviewtobottom, to extend the web view besides the bottom safe area.
• Code cleanup.
• Remove unused or deprecated code.

Testing

I've tested all the possible configurations available with the web UI.

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[flexaddicted]

@NiklasMerz hope this PR will help to improve this plugin for future changes...there is a lot of work to be done but I think this is just a start.

[qwertychouskie]

Would this by any chance resolve #901?