Migrate iOS Keyman Engine to Swift

Toolbar UI / setActiveKeyboard API interaction bugfix

The default sample languages left out a region for English, so it wasn't appearing in the toolbar UI.

Tweaks the new return value's behavior.

Mostly incorporates the 'only set active keyboard if old one was removed' request, though there's an occasional issue with the active keyboard mysteriously persisting.

`removeKeyboards` API function validation + enhancement.

Update to Android Studio and Gradle 3.0

Extended the test slightly and implemented the 'return true/false' component mentioned in the issue.

addKeyboards parameter property:  'language' -> 'languages'.

Sets init param 'attachType' to 'auto' for all devices.

Per Android Studio 3.0 [Release Notes](https://android-developers.googleblog.com/2017/10/android-studio-30.html)

-Update gradle version
-Change deprecated `compile` dependencies to `implementation` or `api`
-Change maven repositories to google (triplet plugin still on maven)
- Update readme instructions for using the engine

[Mac]: Prevent Keyman processing command keys

Cherry picked a few small changes from "mac compatibility" branch to fix bug whereby command keys were sometimes causing characters to be output.

name/id mismatch in MergeKeyboardInfo