Make sure there is only 1 debit and 1 credit line #5352

* Created 2 function fields to hold debit and credit lines.
* Added num2words as a dependency.
* Do not print check until move is posted.
* Make check number readonly when state is posted.
Merge pull request #4 from aroraumang/feature/task-5352

Make sure there is only 1 debit and 1 credit line #5352
Minor changes #5352

* Exclude field 'check_number' from check modify validation
* Show check number field on change of journal
* Changes to validation of move lines