Add dt (delayed tee), like tee but can output to the file that's being read from (for example sort foo.txt | dt foo.txt).

- Get just HELM_HOME from .bashrc.

- No more prerun files, remove said code.
- Set PS1 during __prompt (called by BASH_COMMAND everytime the prompt
is going to be shown).
- Consistent calculation of runduration across __prompt and
__command_notifier.
- Open bug: the exit status is shown until a new command is run.

This reverts commit 208c1bcc. Now all
commands are monitored.

- Use notify-send to notify on finished (successfully or not) long
running commands (all commands, not just those with monitor).
- Move all Bash specifics together, under the if shell==bash clause and
to the end.

- Add region alias for configured (profile) region.
- Add metadata-region for outputting the region from the EC2 metadata
service, moved from .bashrc (no longer exported as AWS_DEFAULT_REGION,
not an issue since it could only be used in EC2 instances and not for
local use, it was there mainly as a reminder for me).
- Add ecr-login instead of a shell alias, works the same.