consolidate sections on translation, internationalization, and release management

[cfm]

Beyond the scope of #86, I think we can consolidate and streamline the documentation of:

1. how the SecureDrop Server and Client are internationalized;
2. how translators translate and review their strings; and
3. how maintainers manage their releases.

The pre-#86 documentation was highly specific on mechanics, of which there are fewer now. The priority now should be to create consistent expectations for each of these roles and processes across applications.