shell boilerplate could be automatically added when building in devmode

[Nish Aravamudan]

It becomes quite common while first snapping an application to add something like:

apps:
    shell:
         command: bash

parts:
    bash:
         plugin: dump
         source: /bin/bash

[ this might not be exactly correct, just wanted to document the idea before EOD ]

It feels like this could be a builtin/transparent addition, perhaps specifically when building in devmode? It makes for much easier debugging of issues/environmental conditions.