Add get_selections() and set_selections() for dpkg.

This module will enable to freeze a package at a certain version, with the "hold" state.
Add TODO, amend later... FIXME.
Merge my dpkg-selections branch with develop.

Resolved conflicts in modules/apt.py.
Fix merge mistake.

urllib2 and json is part of standard Python.
Use yaml.safe_load()
Add another TODO
Use code-block

As per @terminalmage suggestion.
Added mknod functionality for fifo pipes, block devices, character devices, and ancillary functions to the salt file module.
Merge remote-tracking branch 'upstream/develop' into feature_mknod
Syntax of versionadded
Merge pull request #6998 from holmboe/patch-1

Syntax of versionadded
Updated Salt version requirements for Formulas
Changed package-map.jinja references to map.jinja
Fix #6963

we don;t need to bother with yaml if the type is not string,
because the type is already defined.
Remove extra white-space.
docstring formatting in ps module
move seed functions into seed module from img
Remove miss-leading exception.
add lxc module
Merge pull request #7005 from s0undt3ch/develop

Remove extra white-space.