Add support to "set -euo pipefail"

[NN---]

The strict bash mode is not supported fully in oh-my-bash.
There are issues in the code itself and in the prompts.

Reproducing:

$HOME/.bashrc

set -euo pipefail

OSH_THEME="powerline-multiline"
oh-my-bash.sh

[akinomyoga]

set -e shouldn't be turned on in an interactive session. The so-called strict Bash mode is practiced in independent Bash script programs. On the other hand, set -u and set -o pipefail are also useful in interactive sessions. I don't have time to check, but could you check if the issues persist with set -uo pipefail?