Allow statemented item cancellation prior to reconciliation [#86772]
dry the constant
Clear statement on #update_account
Updates for new account move and cancellation behavior

[#86773]:
* When moving a statemented and unreconciled order_detail from one PO/CC
  account to another, the order_detail should be removed from its original
  statement (this should also remove the statement date, which is covered in
  [#86774]).
* When cancelling a statemented and unreconciled order_detail, the order_detail
  should be removed from its original statement (this is clarified in [#86774],
  in that it may remain on its statement if cancellation fees apply).

[#86774]:
* When an order_detail is moved to a different account, its statement date
  should be removed (be nil).
* When an order_detail is cancelled and the item has a cancellation cost, the
  order_detail should remain on its statement with an updated cost (that is,
  the cancellation fee is applied to the statement).
* When an order_detail is cancelled without cost, either because an admin
  waived the cancellation fee or the item has no cancellation fee, the
  order_detail should be removed from its statement (be nil).

[#86775]:
* When a statemented order_detail is moved from one PO/CC account to another
  PO/CC account, the order_detail should be removed from its original statement
  and then become available to be statemented again (rebilled) under the new
  account (in other words, it should appear under "Create Statements").
Style updates
Remove StatementRows when clearing statements
Test for cancellations without a set fee
Use AR to find rows for an order_detail
Style and convention updates
Update spec descriptions and organization
Merge pull request #141 from tablexi/86772-cancel-statemented

Allow statemented item cancellation prior to reconciliation [#86772]