Move color settings from taskrc to default.theme

[d2718nis]

Issue

As previously discussed, it would be beneficial to separate the default color theme from other configuration settings in taskrc. This change would ensure that new color settings don’t unintentionally bypass no-color.theme in case it omits them by mistake. Separating color settings would also improve the organization of configuration files.

Solution

Relocate all color. related settings from the default taskrc template to a new default.theme file. Use include default.theme to apply these color settings, like here.