Make Added QT_PLUGINS_DIR to tools.mk since it is easier to notice

while upgrading Qt SDK versions
Make externalize linux_standalone target from the main makefile
Removed QT_PLUGINS_DIR defenition from the Makefile.linux
Make added QtQuick to linux builds
Makefile.Linux deleted unused definition
Packaging: include tools.mk for the packaging system

This pulls in the main shared variables like the QT_SDK_DIR
Tools: system-id should not define ROOT_DIR

This file should do what it says - identify the system
type. In addition, it wasn't actually finding the ROOT_DIR
correctly, it was finding the directory above the current
directory.

Move defining ROOT_DIR into the main Makefile like it is
with package/Makefile
Merge pull request #1290 from TauLabs/linux_packaging

Linux packaging