Use the term "component" everywhere in the docs

Replace the following terms with "component" when possible in the docs:

• QML type (do not use)
• Item (use only when you mean the QML type called "Item")
• Import (do not use as UI text, will be visible in code)
• Qt module  (do not use)
• Qt/QML library (do not use)

We will still use the word "module" to mean a container for components and functions (QML module).