Choose what parts of host filesystem should be writeable/overlaid

[carlpett]

Is your feature request related to a problem? Please describe.
(Very new toolkit user, let me know if I misunderstand something)
Currently, the toolbox appears to pass a fully rw-mounted /home/myuser into the container. This has the drawback that the tools I was hoping to isolate within the toolbox still writes stuff all over my host environment.

Describe the solution you'd like
Ideally, the home directory is read-only or has some type of overlay (not sure about the feasibility of this) for writes.
Additionally, I'd be able to specify directories (probably subdirectories of home) that should be writeable and reflect to the host.

Describe alternatives you've considered
None that seem to work :)

Additional context
N/A

[debarshiray]

Duplicate of #183