closes #41

closes #52

The mxid input will not prevent the user from entering any invalid
value.

closes #22

closes #11

- Adds detection for duplicate events

closes #46

Basically reverts the last font related commits since pointSize isn't
as reliable as pixelSize.

Also some layout values (margins, spacings) have been moved out to Config.h.

* Validate both inferred and explicitly entered server addresses by attempting to call the /versions endpoint
* If the domain from the mxid fails validation, try prefixing it with 'matrix'
* Only show server address field if address validation ultimately fails

- Fixes small font issue on MacOs

Minor stylistic refactoring

closes #29

[ci skip]