Allow more than one active task

[arcticicestudio]

The default Taskwarrior limit of active tasks is one. However, there are many use cases where multiple active tasks must be used, e.g. when working on an GitHub issue and the associated PR which are both handled in separate tasks or when working on tasks that are dependent on other tasks.
The limited should be increased to allow to use Taskwarrior for such use cases without having to deal with limitation errors.