Prepare v2.x, branch out v1.x

[maschmann]

Prepare new release v2.x and create branch for v1.x

• Remove LegacyRegisterListenersPass
• Switch version dependency to >= php 5.5
• Switch version dependency for Symfony to >= 2.3
• Move to php 5.4 style array syntax, refactor

[xabbuh]

I am 👎 on refactoring the array syntax. It adds to much noise to the diff imho.