Framework: redux themes contains immutable.js objects

[gwwar]

The themes module uses immutable.js. Mixed usage is blocking redux state persistence in #2754 since that section of the tree should be an immutable.js instance rather than a plain js object. When redux state is deserialized, you will see errors like the following:

Inspecting reduxStore.getState().themes shows:

[ehg]

Is this a bug? We're using immutable.js data structures :)

[gwwar]

@ehg maybe bug is a little harsh for this one. Feel free to chime in on #2754 and comment on whether we should push for using immutable.js everywhere, allowing it on sub trees, or if we should stick with plain js objects. ;)

[gwwar]

I went ahead and persisted the themes subtree in #2754, @ehg if you have time I'd appreciate some 👀 on if I got the schemas correct in the themes subtree.