WIP: Migration to add missing indexes.

TODO: We need to review if we need these indexes or not.
TODO: We need to add the :name for any indexes that are too long, see #1170

Replaces #1170

I ran the following code in rails console after migrating to get a list of bigint *_id columns without indexes:

```ruby
tables = ActiveRecord::Base.connection.tables
indexes = {}
tables.each do |t|
  ActiveRecord::Base.connection.columns(t).each do |c|
    next if c.sql_type != "bigint" || !c.name.ends_with?("_id")
    index_found = ActiveRecord::Base.connection.indexes(t).any? do |i|
      i.columns.include?(c.name)
    end

    unless index_found
      indexes[t] ||= []
      indexes[t] << c.name
    end
  end
end

indexes.keys.sort.each do |key|
  columns = indexes[key]
  puts [key.to_sym, columns.collect(&:to_sym)].inspect
end
```