CB-12705: Modified (before|after)_plugin_(uninstall|install) to always expect existence of plugin field
CB-12705: Modified (before|after)_plugin_(uninstall|install) to always expect existence of plugin field

 This closes #549

filmaj/cordova-lib,matrosov-nikita/cordova-lib,dpogue/cordova-lib,dpogue/cordova-lib,filmaj/cordova-lib,stevengill/cordova-lib,filmaj/cordova-lib,filmaj/cordova-lib,filmaj/cordova-lib,stevengill/cordova-lib,matrosov-nikita/cordova-lib,filmaj/cordova-lib,purplecabbage/cordova-lib,shazron/cordova-lib,stevengill/cordova-lib,phonegap-build/cordova-lib,phonegap-build/cordova-lib,purplecabbage/cordova-lib,shazron/cordova-lib,stevengill/cordova-lib,matrosov-nikita/cordova-lib,matrosov-nikita/cordova-lib,phonegap-build/cordova-lib,apache/cordova-lib,apache/cordova-lib,shazron/cordova-lib,purplecabbage/cordova-lib,matrosov-nikita/cordova-lib,apache/cordova-lib,phonegap-build/cordova-lib,shazron/cordova-lib,stevengill/cordova-lib,stevengill/cordova-lib,phonegap-build/cordova-lib,dpogue/cordova-lib,dpogue/cordova-lib,shazron/cordova-lib,dpogue/cordova-lib,apache/cordova-lib,phonegap-build/cordova-lib,shazron/cordova-lib,apache/cordova-lib,purplecabbage/cordova-lib,dpogue/cordova-lib,purplecabbage/cordova-lib,purplecabbage/cordova-lib,matrosov-nikita/cordova-lib