makeconf.py: Adds disable and enable functionality

To allow users to momentarily allow portage to "forget" an overlay
dir, the ability to disable and then re-enable an overlay has been
added.

X-Gentoo-Bug: 512316
X-Gentoo-Bug-URL: https://bugs.gentoo.org/512316
reposconf.py: Adds disable and enable functionality

To allow users to momentarily allow portage to "forget" an
overlay dir, the ability to disable and then re-enable an overlay
has been added.

X-Gentoo-Bug: 512316
X-Gentoo-Bug-URL: https://bugs.gentoo.org/512316
repoconfmanager.py: Adds disable and enable functions

X-Gentoo-Bug: 512316
X-Gentoo-Bug-URL: 512316
db.py: Implements disable and enable functions

X-Gentoo-Bug: 512316
X-Gentoo-Bug-URL: https://bugs.gentoo.org/512316
api.py: Adds disable and enable repo functions

X-Gentoo-Bug: 512316
X-Gentoo-Bug-URL: https://bugs.gentoo.org/512316
cli.py: Adds disable and enable cli functions

argsparser.py: Adds --disable and --enable cli args.

X-Gentoo-Bug: 512316
X-Gentoo-Bug-URL: https://bugs.gentoo.org/512316
Merge pull request #22 from twitch153/disable_enable


This merge attempts to add disable and enable functionality to layman overlays.
For more info, see:
   - X-Gentoo-Bug-URL: https://bugs.gentoo.org/512316
   - X-Gentoo-Bug: 512316