Added a deprecated warning in the interface/sql/ directory. The database sql...

Added a deprecated warning in the interface/sql/ directory. The database sql dump in this directory is not the current development release and the directory will be removed as the installation related code is now located in the install/ tree. The current sql file is available in install/sql/

interface/sql/WARNING.txt

+
+WARNING
+---------------------------------------------------------------------------------
+
+The SQL dump in this directory is deprecated and is not maintained for a while.
+It does  not contain the latest database tables. The ispconfig3db.sql file 
+in this directory and the directory interface/sql/ will be removed. The latest 
+SQL dump is availabe in the directory install/sql/ispconfig3.sql
+
+Please move any installer related code to the installer/... tree.
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