Theme colors to settings

Now our base colors for themes look like this:

```
export const dark = {
  background: "#3F3F3F !important",
  color: "#DBDBDB !important",
};

export const light = {
  background: "#E5E6E8 !important",
  color: "#325359 !important",
};
```
Maybe it could be useful if we create configuration entry to define them.