At the moment "sticky_notes" works only with MySQL installation of
Roundcube.

People Like me that use however Roundcube with SQLIte will face the
Problem that Sticky Notes dont save any Notes as the SQLite Database
stuff is Missing.

So for thos that have Roundcube running with SQLite and want also have
Sticky Notes all you need to do is openning a shell a do the following

cd  /to/your/SQLite.DataBase
sudo sqlite SQLite.DataBase

sqlite>  CREATE TABLE "notes" ("id" INTEGER PRIMARY KEY NOT NULL,
"nid" INTEGER NOT NULL, "width" INTEGER DEFAULT '0', "height" INTEGER
DEFAULT '0', "pos_x" INTEGER DEFAULT '0', "pos_y" INTEGER DEFAULT '0',
"text" TEXT, "user_id" INTEGER unsigned NOT NULL, "timestamp"
TIMESTAMP NOT NULL DEFAULT '0000-00-00 00:00:00', FOREIGN KEY(user_id)
REFERENCES users(user_id) ON DELETE CASCADE ON UPDATE CASCADE );

sqlite> CREATE INDEX idx_notes_userid ON notes (user_id);

sqlite> .quit;

After this Your Sticky Notes will works the same Way as with MySQL.

Enjoy it.