Get weights of direct & indirect delegations

[jinjagit]

We wish to show a user (of Decidim, in #56) the user's voting weight, which may increase (from a base of 1) due to delegations 'received'.

We also wish to show the user how much of this voting weight is due to direct delegations (delegations where the user has been chosen as a delegate), and how much is due to indirect delegations (voting weight delegated to someone earlier in a delegation chains that have been passed on to the user though subsequent delegation(s)).

Thus, we need absinthe queries / a query that will return these values for a given user.

This will also involve developing separate core functions to perform the needed db queries & calculations. Note that currently, update_vote_weight(vote) in lib/liquid_voting/voting_weight.ex does not differentiate between direct and indirect delegations.

[oliverbarnes]

(Edited issue title to remove implementation detail and just leave concise intent. Makes it easier to parse issues lists)