Support secondary displays

When using Niagara Launcher on a secondary display, as made possible by Android itself, it does not behave correctly.

For one, the launcher asks to be set as the default launcher app, which does not make sense in this context.

Secondly, app started from Niagara Launcher will appear on the main screen instead of the one that Niagara Launcher is one.

// You should call startActivity() with displayId like this:

val launchOptions = ActivityOptions.makeBasic()
launchOptions.setLaunchDisplayId(display.displayId)
val options = launchOptions.toBundle()
startActivity(launchIntent, options)

(Thanks Juhyung for the request)