Removed possibility of reinstalling Instances

see:
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_453
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_452
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_450
- http://git.ispconfig.org/panders/ispconfig3/commit/f7ec00b2f8ba3efc5bdeacef9c813f8a826ae3be#note_449

- http://en.wikipedia.org/wiki/SPDY

- 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).

- Merged language files

- Added warning in the interface when a path for a shelluser is set that is outside of the website docroot.
- Added security settings feature to allow the root user of a server to control most aspects of whet the admin user of the controlpanel is allowed to do in system settings. This is especially useful for managed severs where the ispconfig admin user and the root user of the server are different persons.

- Added missing option in centos dovecot.conf file

- Updated version number to 3.0.5.4rc1

- Make sure the correct sys_groupid is saved for web folders and web folder users.