fixed switchSides()

updated to Symfony 3.4

refreshed

Removed default parameters from js (non-compliant with ECMAScript below

Added to unit tests

added survey link to game over dialog

Added swap for computer opponent's pawn

Live version - production environment

fixed fen to/from array bugs

added fenHelper.js

added to tests

added to tests

added to computer opponent

added difficulty slider for computer opponent

fixed js bug with array copy i.e. arr.slice()