Added Filtering by Label

## Description and Impact
Allows For filtering by label

## Rollback Plan
* To roll back this change, revert the merge with: `git revert -m 1 MERGE_SHA` and perform another deploy.

## URLs
> Links to bug tickets or user stories.

#### Risk Level:
- [X] Low
- [ ] Medium
- [ ] High


This can just be

```ruby
pull_ids = @pull_requests.map(&:id)
```

And then your scope in Label can be:

```ruby
scope :with_ids, lambda { |pull_ids| (where("hubstats_labels_pull_requests.pull_request_id" => pull_ids)) unless pull_ids.blank? }
```

Otherwise that's another SQL Injection vulnerability point.