Cleaned up Documentation and User state

if you set an alternate prime_group this would break, replaced {{ name
}} with {{ user_group }}

had the prime group and ssh keys values as another dict. fixed.

Changed Private keys to have content within pillar rather than the salt
file repository.

Changes sudoers entry to get values from pillar rather than assuming
all sudo users want root.

Revising example pillar to add a minimal required values and a full
list of available values

SLS no longer fails for multiple groups

possibility to define alternate user`s prime group

Fix Undefined jinja variable error with Salt 0.17.1

Ran into an error with Salt version 0.17.1:
Rendering SLS users failed, render error: Undefined jinja variable; line 32

After finding https://github.com/saltstack/salt/issues/8245, and working on
line 32, I surmised that line 28 might be the actual cause of the issue.

I just added a quick check to see if uid exists in user, just as the user uid
line does.

better sudoers support & default gid

add support for sudouser being False.
change to adding sudoers config to /etc/sudoers.d/<user>
adding the removal of /etc/sudoers.d/<user> on user removal or switching to sudouser being removed or set to false

Fixed user default shell source

Pulling 'shell' from pillar globally makes no sense, probably a mistake; pulling it from user instead.

Quick example of absent users

Fix requisites for user state

group requisites were wrong. They required {{ group }}_group, while {{ group }} was the actually added group.

Restructure according to new guidelines.