public Builder addAllowedApplication(@NonNull String packageName) {
            mConfig.allowedApplications.add(packageName);
            return this;
        }
Adds an application that's allowed to access the VPN connection.

If this method is called at least once, only applications added through this method (and
no others) are allowed access. Else (if this method is never called), all applications
are allowed by default.  If some applications are added, other, un-added applications
will use networking as if the VPN wasn't running.

@param packageName The full name (e.g.: "com.google.apps.contacts") of an application.
@return this {@link Builder} object to facilitate chaining method calls.
netbare-core/src/main/java/com/github/megatronking/netbare/NetBareConfig.java