iOS refactoring

[MagTuxGit]

I supported my own fork last year and decided to switch back to the original version.

This PR doesn't change any functionality. I made these changes when I added links stream support, and now that part was deleted but refactored code left.

• removed semicolons (swift doesn't need them)
• removed initialisation to nil (it's done by default)
• switch case statements refactored from String to enum because it's much better in swift
• removed Class.init() call because it's redundant for simple initialisation Class()
• ChannelLink changed to ChannelText (dart and swift), because we share text, that can be link as well but not always