Manipulating Linux /etc/group group members (Ref: Issue# 11102)

(1) modules/groupadd.py : Extending by adding three new functions.
adduser, deluser, members . For now it assumes an OS command ‘gpasswd’
is available
.

(2) states/group.py : states.group.present state function is refactored
(along the lines of states.users.present)  to support the following new
options.
  - addusers
  - delusers
  - members

This patch is for review now. This  is currently tested on CentOS(RHEL)
distributions.
Old group.present() state function is renamed as present_old() for now.
Refactor and modularize of the loader interface, adding Map to pyobjects

The problem with using the loaded states (see commit cc8539f) is that
you can end up in situations where a particular state doesn't exist for
whatever reason. This prevents you from building states freely (see
ticket #10918).

The refactor focuses on breaking out the `gen_functions` function into a
number of smaller reusable functions so that pyobjects can load all of
the states and still process `__virtual__()` and `__virtualname__` in a
way that makes sense for building states. After all pyobjects is just
compiling a high state data structure, if a state is available or not
during application time is up to the minion.

As part of this refactor I have also updated all of the inline comments
in the loader to be more consistent with the way things are actually
working now (such as `__virtual__()` returning a string being
deprecated).

There are also some pep8 fixes to the loader file.

Fix #10918

----

This also adds a new feature to pyobjects named `Map`, which allows for
definition of grain dependent data in a pythonic way -- using inner
classes.

----

Lastly this ditches the instance based registry and instead uses a class
based approach like a singleton.
Add salt-git-ssh script to pass the ssh identity to the git command.
Use salt-git-ssh script as the GIT_SSH command for git when using
private keys on ssh based repositories.
Removed unused import tempfile.
Moved git wrapper script to the package templates directory
Fixed templates package reference in git module
Don't use tokens if euid = 0
If a token is present, first attempt to use .root_key to auth.

Fallback to token if that fails.
Initial addition of the nftables state, used to manage nftables via a salt state.  Some cleanup and additional functions added to the nftables module, including the build_rule function which is used by the state.  Some clean up in the iftables module as well.
Rather than relying on dictupdate to merge the pillar and defaults data, first try to get the value from the pillar. If that fails, try the defaults data, and if that fails -- use the default variable passed to the function.
Using .format to build the pillar key as requested
Updated the understanding yaml page to remove a typo.
Merge pull request #11253 from gravyboat/develop

Updated the understanding yaml page to remove a typo.
Add worker behaviors
move worker creation into behaviors
whitespace
Merge pull request #11248 from garethgreenaway/develop

Initial addition of the nftables state and cleanup
Merge pull request #11251 from bigkraig/simplify-defaults

Don't rely on the dictupdate for defaults.py
Clean up workers