Added filtering by desktop environment,
added fallback repository version (trusty).

	modified:   run-installer
	modified:   ubuntu_libraries/code_and_text_editors.sh
	modified:   ubuntu_libraries/install_codecs.sh
    modified:   ubuntu_libraries/install_kernel-headers_and_infrastructure.sh
	modified:   ubuntu_libraries/internet-applications.sh
	modified:   ubuntu_libraries/media-tools.sh
	modified:   ubuntu_libraries/office-tools.sh
	modified:   ubuntu_libraries/sync_and_download_tools.sh
	modified:   ubuntu_libraries/system_tools.sh
	modified:   ubuntu_libraries/ubuntu_and_debian_package-management.sh
	modified:   ubuntu_libraries/user_xdg-settings.sh
	modified:   ubuntu_libraries/virtualization.sh