[GNC] Notes (few other) fields should be editable even after posting invoice

[Amish]

Hello,

There was this fix implemented in Gnucash which inadvertently created 
issue for me.

This was the bug report which was marked RESOLVED FIXED.
https://bugs.gnucash.org/show_bug.cgi?id=797168

But this fix created issue with respect to my GST filing and tracking. 
So I counter opened a bug report last month to fix this, by partially 
reverting it.
https://bugs.gnucash.org/show_bug.cgi?id=797400

I also created pull request on Github for the same:
https://github.com/Gnucash/gnucash/pull/580

Its been one month but since bug report or PR are not reviewed and my 
GST tracking is affected completely. Hence I am posting the same here in 
mailing list.

Here is copy-paste of the description from the bug report that I had filed.

Before Gnucash 3.6, I used to track customer/vendor conversations/issues 
OR GST related and other important points via Notes field of invoice / bill.

Now since Gnucash 3.6 these fields are no more editable, unless I unpost 
the bill.

This does not make sense. Why cant I add notes after bill was posted? It 
does not cause any harm in invoice values. So locking the field is 
unnecessary.

It was so helpful for GST (India) tracking too.

Once I report the invoice to Government portal, I would simply add 
#GSTFILED in Notes. Similarly when my vendors upload their invoices 
(where I am buyer), I would mark those bills as #GSTMATCHED too.

Anytime in future if I wanted to check if there is any invoice / bill 
that is not reported by me (or by my vendor) - I would simply "Find bill 
/ invoice" where notes did not contain #GSTFILED or #GSTMATCHED

This made tracking of my GST returns and GST government filing very easy.

But now that Notes field is un-editable... every time I have to unpost 
the invoice / bill and add note and then post the invoice / bill again. 
(messing up customer payment too). This is not really needed.

Similarly under "Billing information"  - Edit button under Customer / 
Vendor was clickable. This "Edit" also does not affect actual Invoice OR 
bill values. But it helped me find GST number, Phone numbers, Email 
address (and other details) of Customer / Vendor easily and instantly.

Otherwise just to find customer detail - I have to go all the way to 
Customers Overview - Search customer, right click and then Edit. 
(unnecessary three or more clicks and scrolling of screen)

Since Notes field and Edit customer under posted Invoice / bill - does 
not change anything related to Invoice or bill values.. they should be 
made Editable. So that adding notes (after posting) becomes easy and 
obtaining customer information is also fast.

Please re-consider the change and make them editable again. Otherwise it 
handicaps few nice features.

Please review PR, the link is given above.

Thank you,

Amish.