Add dark theme based on SVG graphics for UHD displays

[sm-shaw]

Is your feature request related to a problem? Please describe.
The older version of HammerDB, v2 had a dark theme, e.g.

When SVG graphics were used for UHD displays, the dark theme was not replaced.

Describe the solution you'd like
A dark theme should be reintroduced using SVG.

Describe alternatives you've considered
The previous PNG graphics are only suitable for e.g. displaying X windows across slow networks.

Additional context
The following are example screens for the dark theme based on the same breeze theme used for the current interface.

[sm-shaw]

Database metrics screens, currently Oracle and PostgreSQL will also be updated

[sm-shaw]

Oracle database metrics with additional fixes for dark theme

[sm-shaw]

Updated PostgreSQL metrics

PostgreSQL on Linux example