Add an Applescript .app to the DMG to allow easy installation to ~/Applications folder and optionally add Jalview to the Dock

The macOS DMG installer follows the highly standard installation process for many macOS apps.
That is, it presents (in a styled Finder window) the application, a link to the /Applications folder, and a suggestion (in the form of an arrow) that the user drags the application onto the link. This action copies the application to the /Applications folder.

[as reported by Geoff:]
For a user with no administrator privileges, and no access to, e.g., sudo, the attempt to drag the application into the /Applications folder fails.

For such a user the best option is to create an Applications folder in their home directory and copy the application to there. macOS expects this folder (although it doesn't exist by default) and will look for file associations, icons, etc in .app bundles that appear there as it does for /Applications. This is not necessarily a straightforward task for users so an Applescript to do this for the user could be included in the DMG Finder window. Unfortunately a symbolic link to ~/Applications cannot exist generically, so the Applescript can be used to determine the home directory of the user activating it and proceed from there.

Furthermore, the Applescript app could add the application icon to the user's Dock. This would fix a missing piece of functionality since the DMG was introduced for Jalview 2.11.0.