Added support for commas in the list attribute

Basically I was used to doing `export CAPSULE_REPOS=local,central` and tried to apply the same value to the `Repositories` manifest entry, namely, `Repositories: local,central`. However this does not work, as capsule only supports spacing here, so you would need `Repositories: local central`. Personally I think it should be consistent, it just makes things easier for users.

The change makes it so `Repositories: local central`, `Repositories: local,central` & `Repositories: local, central` works.

Also for mistakes such as the following work too:

`Repositories: ,local`
`Repositories: local,`
`Repositories: local, ,`
`Repositories: , local`