Add an prompt to install the required dependencies after generating coafile

This could be another step in increasing automation. We can generate a shell script file that has commands to install the dependencies of all the bears in the written ".coafile" which are not already installed on user's system. The user can then modify (if he wants) and run the script to install the dependencies.

Not sure if coala does this already?

status/needs design

Start by tracing the coafile-generation flow in this repository and review how bears and their dependencies are represented. Decide how missing dependencies should be detected and how the generated shell script should be presented for user editing and execution. Done means the design is settled and the generated output covers the stated dependency-installation workflow.

Written by the indexing model from the issue text.