Add "Check for update" from toolbar menu

Although this feature is already implemented in boards and libraries, the compiler itself doesn't have such a mechanism. I'm aware that compiler checks for new version at certain time "maybe at startup", but it would be nice to allow user to check for newer version "especially for stand alone version or night build"

Start by inspecting how update checks are implemented for boards and libraries, then trace the toolbar menu in the Arduino IDE 1.x compiler. Done means a user can manually check for a newer compiler version, including in standalone or nightly builds.

Written by the indexing model from the issue text.