Accounts `by_group` should omit empty groups, render empty UI about maybe

[zachgoll]

@claudey you are correct, I'll go ahead and close this issue out.

This was for a prior version of the UI, so I think #707 actually addresses all of it!

[zachgoll]

Here's where everything is being grouped:

maybe/app/models/account.rb

Lines 46 to 61 in c7b336d

	def self.by_group(period = Period.all)
	grouped_accounts = { assets: ValueGroup.new("Assets"), liabilities: ValueGroup.new("Liabilities") }
	Accountable.by_classification.each do |classification, types|
	types.each do |type|
	group = grouped_accounts[classification.to_sym].add_child_node(type)
	Accountable.from_type(type).includes(:account).each do |accountable|
	account = accountable.account
	value_node = group.add_value_node(account)
	value_node.attach_series(account.series(period))
	end
	end
	end
	grouped_accounts
	end

And to fix this, we could probably add an empty? method on the ValueGroup class:

maybe/app/models/value_group.rb

Lines 37 to 40 in c7b336d

	def value_nodes
	return [ self ] unless value.nil?
	children.flat_map { |child| child.value_nodes }
	end

Something like:

def empty?
  value_nodes.empty?
end

[claudey]

@zachgoll I think #707 fixes the first part of this issue, the Empty State problem to address.