Add Dark (Arduino) theme

[Logicer16]

Is your feature request related to a problem? Please describe.
There is only a 'Light (Arduino)' theme along with the Theia themes, making it odd that light is specified.

Describe the solution you'd like
Add a "Dark (Arduino)" theme. In theory, it would be one that follows the main colours of the light version, but replaced the white backgrounds with black/grey ones and replaces the blank text with white text.

Describe alternatives you've considered
While there is the "Dark (Theia)" theme, it does not feel like an Arduino theme due to the colour scheme.

[Logicer16]

Added in #991