Move configuration to its own form and menu item

So that the report configuration is consistent between the Sale,
Purchase and Stock modules the configuration for the module has been
moved from the Purchase Configuration form onto a form of its own.  A
menu item for this new form has been created under the Purchase /
Configuration menu.

The name of the form and classes that make it up have been made
consistent across the module.
Prepare release 3.4.0

Version number increase and change log update to make the package
ready to be released as version 3.4.0.
Merge branch '3.4' into develop

Merge the changes that were made for the 3.4.0 release into the develop
branch.