Proposed fix for #3929 (letsencrypt can not be activated when a new website gets created). Needs testing.

- hooked ssl and ssl_letsencrypt checkboxes

- added limit for letsencrypt and directive snippets selector to client limits
- hide ssl tab if letsencrypt is selected

- Directive snippets can now be made available to clients; clients can select an available directive snippet for a website - the appropriate snippet will then be written to the vhost configuration file. This is useful for example on nginx where clients have no access to the Options tab of a website.

- Added HHVM to "Default PHP Handler" field (server configuration).
- Fixed "Unable to load the server configuration from database." error when running server.sh.
- Fixed Javascript (accordions weren't working anymore, directive snippets and other placeholders couldn't be added anymore).

Completly same functionality as VHost-Subdomain, not to disable if already existing vhostalias-somains in system.

- Fill IP select fields with IP from correct server even if the user's default web server is another server. Otherwise if the user opens the web form, the wildcard * is selected, and if he changes the tab, the wildcard is saved instead of the correct IP so that the website will no longer work.

Removed workarounds

- Added fields to client, reseller and website to show when a record was added and by which user