Add `verbose` flag to show complete output

Two different use cases to consider:
## "text/plain": Use different rendering if not in a TTY (if piping output into a log file, build server, ...)
- Don't show fancy output containing a lot of ANSI control characters, but rather simple plain text only
- See also: SamVerschueren/listr#11, SamVerschueren/listr#12
- Extending `listr` might be the best way to go
## "verbose": Show complete output of a task instantly (for debugging purposes)
- Might mean that tasks cannot be run in parallel