Allow more control over invocation of completion models when automatic invocation is not used.
- Starting several models at once
- Using an invocation type other that ManualInvocation (important for CodeCompletionModel::MatchReaction::HideListIfAutomaticInvocation)
- Clean way to retrieve list of all registered models (including the KateKeywordCompletionModel)
Combined, these additions allow to inplement a complete custom version of KateCompletionWidget::automaticInvocation().