Micro: removing UTF-8 magic comments

Unneeded in Ruby 2.0
Microoptimize: hours_worked

Saving some memory and some time:
- Query for punches now uses "pluck" to retrieve
only the wanted values (entrance and punched_at)
- Calculates hours worked on the fly, without using a
extra "fixed punches" array
Added README.md

The Rails one was ugly.
Use strong parameters in controllers

Instead of blindly accepting everything, use Rails 4 strong parameter
feature and restrict what can and cannot pass.
Micro: remove unneeded helper in template

Javascript is loaded anyway.
Add option for partial reports of current month

- Accessible through a extra parameter in the report action
- Also fixed a error in the users scripts