db.php: initialize a PDO connection to db
    - dbClose(): close connection
    - dbLastInsertID(): last insert id
    - dbQuery(): prepare a statement and execute it
Signed-off-by:Georgi Krastev <joro.kr.21@gmail.com>
repaired connection string from MySQL to PGSQL
Signed-off-by:Georgi Krastev <joro.kr.21@gmail.com>
removed charset from connection string
Signed-off-by:Georgi Krastev <joro.kr.21@gmail.com>
changed db user password
Signed-off-by:Georgi Krastev <joro.kr.21@gmail.com>
db.php: added function
    - dbGetPDO(): get the global PDO connection object
Signed-off-by:Georgi Krastev <joro.kr.21@gmail.com>
Added example JSON objects