Per-user reblog hiding implementation/fixes/tests

Note that this will only hide/show *future* reblogs by a user, and does
nothing to remove/add reblogs that are already in the timeline. I don't
think that's a particularly confusing behavior, and it's a lot easier
to implement (similar to mutes, I believe).

spec/controllers/api/v1/accounts/relationships_controller_spec.rb

@@ -32,7 +32,7 @@ describe Api::V1::Accounts::RelationshipsController do
         json = body_as_json
 
         expect(json).to be_a Enumerable
-        expect(json.first[:following]).to be true
+        expect(json.first[:following]).to be_truthy
         expect(json.first[:followed_by]).to be false
       end
     end
@@ -51,7 +51,7 @@ describe Api::V1::Accounts::RelationshipsController do
 
         expect(json).to be_a Enumerable
         expect(json.first[:id]).to eq simon.id.to_s
-        expect(json.first[:following]).to be true
+        expect(json.first[:following]).to be_truthy
         expect(json.first[:followed_by]).to be false
         expect(json.first[:muting]).to be false
         expect(json.first[:requested]).to be false