Added new features and made several fixes

[adnahmed]

1. add function to rerender annotations when changed.
2. maintain history of annotations added/removed.
3. add RemoteStore/RemoteStoreUser that can sync with server to store annotations
4. add ability to render an image annotation (for signature preview)
5. add ability to add text in rect annotations (for marking)
6. add option to make annotations exlusive (not cross boundaries)
7. added a hook to call after adding an annotation
8. added ability to preview/unpreview signatures on rect annotations.
9. fixed build scripts
10. miscellaneous fixes and comments.