[M108 Migration][VD] Add API to for malicious page warning showing.

[M108 Migration][VD] Add API to for malicious page warning showing.

Add ewk_view_html_string_override_current_entry_load to show
warning page for web browser security.
Fix issue occur in the following scenario:
1. Access www.google.com in org.tizen.browser.
2. Access malicious url, then wbs alert page is shown.
3. Press "goback" button, browser show malicious url page,
   not the previous page of www.google.com.
Treat the alert page and malicious page as the same navigation entry.
Add a new ewk API to show error page when malicious url detected.

Reference:
- https://review.tizen.org/gerrit/283452/

Change-Id: I0f9a4467a7a3d5a0af54189d9b79ced320a45188
Signed-off-by: feifei08.liu <feifei08.liu@samsung.com>