Added EDataBookCursor & EDataBookCursorSqlite

Added EDataBookCursor & EDataBookCursorSqlite

EDataBookCursor is an abstract class with the mid-level cursor APIs, it
takes care of responding to D-Bus APIs and provides an API which can
be used in Direct Read Access mode but does not implement the actual
cursor state and navigation directly.

EDataBookCursorSqlite is a cursor implementation which uses
a EBookBackendSqliteDB cursor to implement the EDataBookCursor
methods.

This patch also adds the E_CLIENT_ERROR_END_OF_LIST error, intended
to be a generic boundary error when a client api reaches the end
of some list of data (this is used by the cursor API of course
to report an error when trying to navigate the cursor outside of the
list boundaries).