Preserve users PS1

[mbmcmullen27]

PS1 env var is unset in subshells, we could potentially read it from the bashrc but it could be set there around conditional logic

• we could instead use helper functions to make the custom one easier to customize, but that will almost surely be less robust
• I think the best solution might be to allow it to be set with functions that escape the special PS1 chars in the same way we did manually in the set-template function
  • would need to write something almost like a PS1 parser