lxdock 0.5 release tasks

[robvdl]

• Bump version to 0.5.dev
• List new maintainers in README and Documentation but keep original maintainers there too
• Fix lxdock shell -c issue before we release (issue lxdock shell -c does not use login environment and sets incorrect SHELL #147)
• Document idmap changes
• Document default user feature (todo)
• Document ansible user change (ansible should not run as root by default)
• Document network timeout setting (extras)
• Document vagrant box for running tests locally
• Check if contrib/completion is still up to date (have we added any new commands, new argument?)

[mtausig]

With #169 merged, we can check the second last box.

[robvdl]

Yeah we really should try to make the 0.5 release happen. I got so busy at work over the last year the lxdock project just didn't move (until recently again).

[robvdl]

See #184