Problem
---------
When creating and editing a bank account, a creation model pops-up to
edit the bank account information. The previously entered bank account
must be entered again which isn't user-friendly. 

Objective
---------
The data entered on the bank account bank account should pre-fill 
acc_number on partner bank pop-up. 

Solution
---------
When create & edit, `name` could be used to pass (in the context) the
value input by the user. However, we want to set the default value of
`acc_number` variable instead. By overriding the default_get method,
we can get modify the context to do just that.

task-3557753

closes odoo/odoo#139211

Signed-off-by: Wala Gauthier (gawa) <gawa@odoo.com>