renaming per terminology decisions

[ehennum]

As captured in internal issue DHFPROD-770

Old New Purpose
functionFile endpointDeclarationFile the property of the initializeModule task identifying a *.api file
generateProxy generateEndpointProxies the task to generate the service class
GeneratorTask EndpointProxiesGenTask the task type that implements generateProxy
serviceBundleFilename serviceDeclarationFile the property of the generateProxy task identifying the service.json
proxyConfig endpointProxiesConfig the configuration of the generateProxy task

[ehennum]

The test invocations of Gradle will need to be revised. Comparing the Gradle unit tests before and after this commit should clarify.

[georgeajit]

No regressions on Jenkins due to terminolgy changes. Manual tests using new terms ran fine, while class generation from .api was being done.