reflect notification status .isNotifying back ...

[kscheff]

... and make delegate didUpdateNotificationStateFor for mock implementation available.

When enabling a notification and sending data via .simulateValueUpdate the data is getting lost until the manager caught up with the enabling. Since the enabling is sent async with a delay to an internal queue it takes an uncertain time until data will be sent. The characteristics property .isNotifying is not updated in mock device implementation.

This fix implements a mock delegation didUpdateNotoficationStateFor: and updates .isNotifying property.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

:white_check_mark: philips77
:x: Kai Scheffer

---

Kai Scheffer seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[NickKibish]

I see that #70 brings the same changes. So I close this PR.