Re-factor: Simplify application handler naming

[Ceredron]

Description

The application handler naming was originally based on CQRS conventions, but we saw that it did not help make the codebase easier to navigate. The query/command distinction maps surjectively to the first verb in the application handler name anyway, and we should free up room in our class names for other elements that may be more useful.
Correspondence has gotten a lot of application handlers, and we will need to find a better way to organize them eventually.

Related Issue(s)

• #{issue number}

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)

[RagnarFatland-Avanade]

Looks good, but this PR should be linked to a relevant Issue.