Introduce `screenkey`

Screenkey is a screencast tool to display your keys inspired by
Screenflick for Mac OS and based initially on key-mon project. It's
useful to create screencasts and is also a powerful teaching tool.
packages_apt: Fix typo in `state` attribute
tasks: Introduce `keepass` tasks

See http://sourceforge.net/p/keepass/discussion/329220/thread/17d1bd26
bootstrap: Simplify setup
playbook: Install `fping` for multi-ping

See http://fping.sourceforge.net/man/
go: Add shell tasks for installing `golang`