Added light and dark theme options in the settings

[lucasriechelmann]

I have added the option to change from Light to Dark theme.
I couldn't get it to automatically change the colours after the setting was changed.
The SSMS need to be restarted for that.
I will research how to get Visual Studio theme colours to automatically change the colours based on that.
For now we can have a dark theme manually set.

[joaoribe]

Thank you so much Lucas for contributing, tt's looking great :)

Whenever you have some time to have a look at:

• refreshing the Theme colour when saving the Settings Form; or
• inheriting Theme from SSMS

Would be great :)
If I have some time will also try to have a look!