Update dev start script (start.ps1)

[pwgit-create]

Description:

1. Update FE jar version to 1.2.1
2. Update BE jar version to 1.8.3

This will aid in improving the experience during future development sessions in the GUI app.

Reference:

1. https://github.com/pwssOrg/File-Integrity-GUI/blob/master/start.ps1#L18
2. https://github.com/pwssOrg/File-Integrity-GUI/blob/master/start.ps1#L19