Add typing for redux actions

[dblatcher]

issue

The application is largely written in js, making the data flow and application state relatively opaque.

opportunity

#1221 adding optional typing for api requests and responses from the apiRequest function, which is used by several Api modules in the "services" folder - eg VideosApi, PlutoApi.

The most common use of these Api modules are in the "actions" folder which are all in js. Having type available for the api responses should allow us to meaningfully type the actions which are being dispatched into reducers, then type what actions each reducer can handle.

approach

To see earlier benefits, it would probably be best to pick a single reducer a type all the functions that feed actions into it, rather than trying to do all actions, then all reducers.