Add a dialog for deleting annotations

[Feuermagier]

Checklist

• [x] I tested all changes and their related features locally or with a test instance of Artemis.
• [x] I documented the Java code using JavaDoc style.
• [x] I documented the changes in the Documentation (/docs).

Motivation and Context

Deleting annotations with the marker view is tedious. Closes #302.

Description

Adds a new command (by default Ctrl+Alt+Enter) that opens a small window (similar to the "create annotation" window) which shows all annotations at the current line. Press Del to select the selected annotation or Esc to close the dialog.

Important: This PR includes the changes made in #313, so I'm going to close the other PR.

Steps for Testing

Start an assessment, focus the editor, press Ctrl+Alt+Enter.

[tsaglam]

@tsaglam maybe test the behavior on MacOS :)

After the fix it seems to work, no issues on macOS.