on iPad, support same keyboard shortcuts as objective-c version

[bmagyarkuti]

The Swift version of Telegram for iOS, which has now replaced the old ObjectiveC version on the AppStore, has no support whatsoever for Keyboard Shortcuts on the iPad.

It'd be great to re-implement keyboard shortcut support, just as it was in the old version. That version had the best support for keyboard shortcuts of any iOS messaging app: it was possible to switch between conversations without using touch input at all.

For example, one could <Tab> Some Contact <Enter> Hey, it's me... <Enter> to start composing a message and send it.