[Tizen] Implement composition mode for Tizen input method framework

This patch adds initial implementation of composition mode.
Composition mode is required for languages where final character could
be produced by combination of keystrokes.

In order to implement composition mode, several SCIM callback methods were
implemented. Most important ones are the following: callbacks that notify client
to show, hide, update and commit preedit string and set of callbacks that are
responsible for input method state management.