Make exception handler comply with HttpKernelInterface

- Don't send response in handleException to comply with HttpKernelInterface
- Added handleUncaughtException which also sends the response
Update Mailer.php

added missing class property
Merge pull request #4075 from janschoenherr/patch-1

Update Mailer.php
Merge pull request #4073 from alprs/fix/exhandler-httpkernel

Make exception handler comply with HttpKernelInterface
Revert "use model->newCollection"

This reverts commit 26e5809a68464387b1544e2d614354f73fc72b07.
Revert "remove find, findOrFail from model, delegate to query builder"

This reverts commit 7f8b07c5b338d071606d4b9b0acf2d956ae2ef4e.
Add back new collection.
Composer improvements