Make UWPX accessible to narrator and other screen readers

[MarcoZehe]

Bevor you create a new issue:

- [ x ] I searched for similar issues and did not find one
- [ x ] I'm using the latest version available in the [Windows Store](https://www.microsoft.com/store/apps/9NW16X9JB5WV)

I'm submitting a...:

• Bug report (I searched for similar issues and did not find one)

Current behavior:

UWPX does not expose any useful information to assistive technologies such as Narrator (invoked with CTRL+WindowsKey+Enter) or other screen readers such as NVDA. Buttons are not labeled, and other controls also expose no useful information. Right now, a blind user can't even log into a server.

Expected behavior:

Labeled controls and otherwise accessible application. More information: Accessibility main page for UWP apps, and especially Expose basic accessibility information.

Minimal reproduction of the problem with instructions:

1. Get started with Narrator.
2. Start Narrator and UWPX.
3. Tab around the interface and listen to what you hear, and don't hear.

Environment:

App Version(s): 
v.0.15.0 <!-- Which version of the App are you using (e.g. v.0.2.0) -->

Windows 10 Version Number: <!-- https://en.wikipedia.org/wiki/Windows_10_version_history -->
- [ x ] 1809
- [ ] 1803
- [ ] 1709
- [ ] 1703
- [ ] 1607
- [ ] 1511
- [ ] 1507
- [ ] Insider Build (build number: )
- [ ] Misc:

Device form factor:
- [ x ] Desktop
- [ ] Mobile
- [ ] Xbox
- [ ] Surface Hub

Where did you got the APP from?
- [ x ] [Windows Store](https://www.microsoft.com/store/apps/9NW16X9JB5WV)
- [ ] Self-build, using a provided release source
- [ ] Self-build, repo cloned at [dd.mm.yyy] <!-- When did you clone the repo! -->
- [ ] Misc, got it from... <!-- Please tell us your source! -->

[COM8]

Thanks for opening the issue.
Will add it to the UI Overhaul (#50) todo list.