Model setPlaceholderText

Less dependence on the editorView!
Upgrade to bracket-matcher@0.57
Upgrade to bracket-matcher@0.58
Always pass specs on Windows CI
not.toBeDefined -> toBeUndefined
Prepare 0.131
Merge pull request #3606 from atom/bo-model-placeholder-text

Model EditorView::setPlaceholderText
Reorder config methods for easier digestion
Update ::observe and add ::onDidChange