* first refactoring on QZXing.pri to group sources based on type of barcode and operation
* Moved the newly created source code groups of functionalities to separate pri file (QZXing-components.pri).
* In QZXing.pri include QZXing-components.pri having previously added as configuration all the available modules to preserve the backward compatibility.
* Deactivate parts of code based on the configuration of the pro file. (Work in Progress).
* fix compilation error
* Fix include issue when only "enable_encoder_qr_code" config is used through QZXing-components.pri
Update example projects to use QZXing-components.pri
Fixed warnings in QZXingFilter.cpp
Removed C++11 requirement from all .pro files
Set compiler warning flags via CONFIG += warn_on instead of using GCC specific switches