Changes in fetch-packages.sh script:

1. Added "getPackage" function which takes the third-party library URL & package name as arguments and checks if that package exists in "/tmp/cache" and if available it copies  it to current directory, else it downloads using wget to "/tmp/cache" and then copies to current directory
2. Fixed naming issue where multiple third-party libraries are using the same name (master.zip for multiselect,SlickGridEnhancementPage) while using wget