Changed answers file
Added task #4
Created new task (#5) + new database

New task is about Concat usage in SQL-injections.
New database is for tasks 4 and 5 to make them stand aside from previous
tasks.
Migrate to MySQLi extension
Improved task #4

The task does not look like #2 anymore.
Selection menu changed to the buttons panel with icons of flags.
Default look now is the 'select all' from the table.
Upgrade task #5

New database
Merge remote-tracking branch 'origin/master'