Restore database -> subscriptions page (using queries rather than subscriptions, and with pagination)

[Venryx]

We had to move away from using subscriptions / live-queries, because the subscriptions table just has way too many rows. (it was causing the app-server to crash, with over 90,000 subscriptions for a user who imported lots of nodes and was thus auto-subscribed to them all)

[Venryx]

Task: Create a new graphql "subscriptions" query endpoint (leave the existing subscription endpoint unchanged).

Details:

• It should have the following params:
  • limit: [integer] The size of the result-set that the caller is requesting
  • after: [string, or null] If provided, the result-set begins after the "subscription" entry with the given id (the "id" column in the "subscriptions" table), to be used for pagination.
• It should sort the result-set, in descending order (ie. newest ones first), based on the "updatedAt" field.
• The response structure should also contain a field saying how many entries were "skipped over" (due to the "after" param), in order to retrieve the response's result-set. (this is used to ensure the "page number" displayed in the UI remains accurate even if new subscriptions get added while the user is progressing through the pages)

[Venryx]

Completed by Alvi. (just merged)