added an auto-increment pk `id` to player

This change was mostly out of the realisation that the player_no gives away a player's role and cannot under any circumstance be communicated with players, so putting the PK in an input field is not possible. To get forms to work without the hassle of looking up players by their alias (which are not strictly unique -- but that's another issue), some other unique identifier is required.
significant rehaul of the preprocessor ecosystem

- using FontAwesome instead of Entypo
- removed pure.css; just sticking with normalize.css
- added and utilising Bourbon.io mixins
- plans to split .scss files into multiple parts
- renamed Mafia::Sass to Mafia::Watcher, which also watches and minifies the JavaScript on changes
- also made some improvements to Mafia::Watcher to make it more decoupled from the calling app

Also fixed a bug related to user login/registration
removed artifacts of old css in html
refactored scss into config, components and layout