upgrade to php7.3 yields warning

[m3eu]

After upgrade to php 7.3 the following warning is displayed in the admin page:
Warning: Use of undefined constant PSHARE_ADMIN_BASE_URL - assumed 'PSHARE_ADMIN_BASE_URL' (this will throw an Error in a future version of PHP).
This also effects the changes for a better UI management, I added a comment in respective pull request.

SOLUTION => ? => replace PSHARE_ADMIN_BASE_URL with MUGSHOT_ADMIN