Only ship in $PATH custom scripts that we intend users to run

Originally created by @intrigeri on #10658 (Redmine)

/usr/local/*bin contains lots of helper scripts that users should not be tempted to run. They should go to /usr/local/lib. Now we won’t have anything serious to forward-port from Wheezy to Jessie anymore, we’ll be testing feature/jessie a lot for 2 months, so perhaps it’s the good time to do it in feature/jessie. Not a blocker though.

Feature Branch: feature/10658-clean-up-path