cleaned up plugin class and divided installer into Installer/CoreInstaller and Installer/ModuleInstaller

removed original Installer
updated tests
refactoring CoreInstaller
moved constant SORT_PRIORITY_KEY to ProjectConfig
changed travis notifications temporarily
cleaned up CoreInstaller
always use Copy as Deploy Strategy for CoreInstaller
moved root package config operations to ProjectConfig
moved redeployProject method to CoreInstaller
updated FullStackTest to use the CoreInstaller and install magento/core:* instead of Downloading Magento
bugfixing
fixed default type in Installer Constructor
cleaned up install and update methods
add another FullStackTest for global install

also extract some of the reused code into an base class for
fullStackTests
add GlobalUpdate test
add some cleanup to global test
use real installer for global test
add own deploy manager object for core installer
simple workaround for coreInstaller update problem
add link to Using composer correctly

 (confoo) by Igor Wiedler
add phpcs as dev dependency to experiment with it