Moving remaining plugins to bootstrapvz/plugins/

Three of the last developed plugins remained on the old `plugins/`
folder. This probably happened because they didn't existed when the
`documentation` branch were created, so they weren't moved when it was
rebased against `master`.
Merge pull request #60 from myhro/fix-plugins

Moving remaining plugins to bootstrapvz/plugins/
Add support for adding APT preferences
Merge pull request #62 from Jimdo/add-support-for-apt-preferences

Add support for adding APT preferences