chmod-based shared folder permission system

[ghost]

ACL-based permission management is complicated doesn't work well. I had an idea today for a simple "just make the damn thing world-readable" system that would be based on chmod and file watching.

Because we would repeatedly chmod -R o+rwX folders, it's better if we limit the number of files it targets, so we'll ask users to indicate which subfolders, in their shared folder, should be world-writable. Something like:

shares:
  - source: .
    dest: /lxdockshare
    writable_paths:
      - some/relative/path
      - another/one

Considering that shared folders are mostly only used in development environments, I'm guessing that making some folders world readable isn't much of a problem. We would, of course, clearly indicate the "world readable" aspect of the thing in the docs.

The process would go something like this:

1. On lxdock up, run chmod -Rf o+rwX on all writable paths, on the host.
2. On lxdock halt, do the same, but on the guest.
3. Add a new lxdock sync command that would behave like vagrant rsync-auto (possibly using entr?). It would chmod on both the host and the guest.

This would replace the ACL system.

Closely related to #46. Ping @robvdl .

[robvdl]

I have to have a think about this, because things are currently working :)

The biggest issue I can see here, is all your git files becoming dirty all at the same time, if you mess with perms in the source root of your project

[shuhaowu]

@robvdl how does this issue translate with the new uid/gid map system. Do we still care about it to be open?