Fixes for QML Basic Types docs

Fixes for QML Basic Types docs

- Standardize the \brief and introductory lines for each type
- Explain that some C++ types match to basic types, e.g. QFont -> font
- Explain that URL values don't match against their input string values
- Fix list type docs and don't encourage its use for custom properties
  (use var instead)
- Remove action since QAction isn't registered as a QML type anymore
- Document that color type has r,g,b,a properties
- Do some other cleaning up

Change-Id: Ie8a2886b938166938618c3a0bf47363f443ee401
Reviewed-by: Chris Adams <christopher.adams@nokia.com>