[ENHANCEMENT] Only propose valid *Test-* or *Task-specific* settings when suite type is defined.

[Snooz82]

If a suite file does contain a *** Test Cases *** section, it is clear that this is a Test Suite so task-specific settings shall not be shown anymore in completion of the settings.

Even though Task Setup is a real synonym to Test Setup and can also be used in Test Suites it shouldn't be used. So stopping the completion would help to keep the code clean.

Also the Error that only either Test Cases or Tasks are allowed (One file cannot have both tests and tasks.) should be better located at the row of the test cases or task section.