Revert #898
Define PRODUCT_NAME
Use PRODUCT_NAME as application name
Discard "framework_name"

We are using "'product_name' Framework" directly in C++, so we should
keep the name consistent in C++ and gyp
Make product_name and project_name configurable

Now users can make use of GYP_DEFINES to custom application name:

export GYP_DEFINES="product_name=MyApp project_name=myapp"
./script/update.py
./script/build.py -C Release -t myapp
docs: Update Application Distribution
docs: Mention the GYP_DEFINES way of rebranding
Merge pull request #962 from atom/fix-rename-bundle

Fix renaming application bundle on Mac