Added proxy-manager dependency

Due to package substitution (composer replace), elcodi/elcodi must
fulfill all the requirements of its subpackages. Doctrine proxy manager
is an optional package used in GeoBundle and CurrencyBundle and now it
must be required from elcodi/elcodi composer.json as well.
Package version range is taken from symfony/proxy-manager.
Removed proxy-manager dependency from Geo component
Merge pull request #271 from elcodi/Fix/proxy-manager-in-root-composer-json

Added proxy-manager dependency