upgrade apps to latest version compatible with running macOS #566
Description
upgrade apps to latest version compatible with running macOS.
Probably requires trying to upgrade if either installed version of app is out of date, or if minimumOsVersion for current store version of app is greater than running macOS version.
Currently, will get a dialog box no matter what, to install a non-current version. "Upgrade" might be for the same version as is currently installed.
See #80 for similar feature for install (& lucky).