Dismiss operation (WPS 2.0.0)

[huard]

Description

Implement "dismiss" operation to stop an asynchronous process.

Could someone split the tasks necessary to get there in small chunks that newbies can work on this ?

For example:

• Create dismiss XML template
• Implement cancel method in processing.basic.MultiProcessing

[cehbrecht]

@jachym Any comments on this issue?

[cehbrecht]

See also #493