Not possible to specify the default handling of keyword arguments

[philthompson10]

The value of the keyword_arguments argument of the %Module directive in generated .sip files is hardcoded to "Optional". The following changes are needed to allow the user to specify a different value:

• an appropriate attribute to be added to the Module model
• the .sip generation to respect the value of the attribute
• the project i/o code to read and write the attribute from and to a project file
• support for changing the value of the attribute to be added to the module properties dialog
• the minor part of the project version number to be bumped
• migration of the older project version must set the attribute value to "Optional".