[feladat @ 252] Added the possibility to select whether MySQL or PostgreSQL should be used. Depending on the choice, a different instruction is displayed in step 3. Also fixed a minor typo.

[feladat @ 251] Fixed a small problem in the database scheme that is created by the install procedure.

[feladat @ 250] Added a check for the existence of the install/ direcory. If it exists, present the user with an error message.

[feladat @ 249] Added a small check to make sure a nice message is shown if the users does not have view access to any zone (in list_zones.php).