Allow edit of old purchases under Inventory

[aniljava]

Purchase entries once entered are non-editable. Allow editing in a case if there is a mistake.

[jkleinsc]

@aniljava this is intentional. The idea is that any adjustments to inventory, including mistakes made entering a purchase would be adjusted via the Adjust button on a location. The reason for this design is that it ensures that any adjustments to inventory have a clear audit trail.

[tangollama]

Agreed. Thanks for the input @aniljava. If you have further concerns re: this issue, feel free to reply. As @jkleinsc pointed out, the process for adjustments vs. edits came directly from user feedback.