Service modularization todos

I've collected some TODOs from the service modularization PR #363 so we don't forget.

@AntonLantukh @dbudzins Feel free to add or remove items from the lists.

TODOs:

[x] Move integration service files into folders e.g., ./src/services/integrations/jwp/InPlayerAccountService.ts
[ ] Refactor entitlement service(s) to align with the integration better
[x] Refactor isSandbox from all service calls (not sure about this yet)
[x] Obtain the access model via integration (by optionally passing the media item?)

Minor TODOs (long term):

[ ] Make integration interfaces more generic for different implementations (currently following Cleeng schemas and APIs)
[ ] Dynamically load and bind integration files in IoC based on directory structure

jwplayer / ott-web-app