Login form will react on `Enter` key as it should

Pressing `Enter` after entering name will change focus to
password
field.
Pressing `Enter` after entering password will act as
pressing the button
`btnLogin`.
Issue #3 resolved.
Exclude mistakenly added (in last commit) nunit from MainProject.
Fix of failed login

Added user is null check
Login form. `Enter` will accept entered username and password.

`Enter` will not change the focus to next control, but instead.
Add to previous commit
Add to previous commit
Merge pull request #546 from qlynn/avtc

Issue #3 - Login form will react on `Enter` key as it should