Create Launcher Files in ~/invokeai

[lstein]

Create Launcher Files in the ~/invokeai directory

To solve the "there's no invoke.bat!" issue, this PR adds a function to configure_invokeai.py to create the appropriate launcher script in the ~/invokeai runtime directory. It is hacky to do it this way, but the configure script has immediate access to the user's selection of the root directory and this seemed more reliable to me than passing the root directory back from the configure script to the install script. Also we can tell the user to run the configure script in order to create the "missing" launcher.

I have tested this on Linux with both the binary and source installers. The Windows version needs extensive testing. In order to make testing work, I have changed the REPO to the branch lstein-config-launch in all the install scripts. They will need to be changed back to main prior to release.