Changing the "SystemChannels.lifecycle" to "AppLifecycleListener"

[GabrielRozendo]

Changing the SystemChannels.lifecycle to AppLifecycleListener

The SystemChannels.lifecycle causes side impacts on whole app and should not be used.
Replacing for AppLifecycleListener

Related to item 1 in #13, quoting:

1. Lifecycle issue

The PR #8 is working as should

but now I need to listen the flutter's lifecycle in my app (not in aptabase's package) and since the package already is doing that and as documented on SystemChannels.lifecycle:

/// The given callback will replace the currently registered callback for this
/// channel, if any. To remove the handler, pass null as the handler
/// argument.
we would lose the feature "send events when app goes to background".
And I've found out the SystemChannels.lifecycle has other unwanted side effects in general.

[lora-explora]

checked out the PR and can verify that Aptabase tracking still works and the lifecycle listeners get called again in the app 👍