Some more Extensions improvements

A few fixes: 
Several UI fixes that streamline the responses.
A fix to a JS error
Leave error output on the screen after an install
Fix to readonly mode to try creation of a composer.json file if it doesn't exist.
Force all composer commands to run in no interaction mode
Fix to composer repositories command that was broken by the format validation
Remove the post install script since this was broken. Needs testing and putting back in when ready.