Add APIs of webview settings.

Add APIs of webview settings.

    API added list:

    ewk_settings_cache_builder_enabled_set
    ewk_settings_uses_scrollbar_thumb_focus_notifications_set
    ewk_settings_do_not_track_set
    ewk_settings_auto_fitting_get
    ewk_settings_auto_fitting_set
    ewk_settings_plugins_enabled_get
    ewk_settings_plugins_enabled_set
    ewk_settings_private_browsing_enabled_get
    ewk_settings_private_browsing_enabled_set
    ewk_settings_link_magnifier_enabled_get
    ewk_settings_link_magnifier_enabled_set
    ewk_settings_uses_keypad_without_user_action_get
    ewk_settings_uses_keypad_without_user_action_set
    ewk_settings_autofill_password_form_enabled_get
    ewk_settings_autofill_password_form_enabled_set
    ewk_settings_form_candidate_data_enabled_get
    ewk_settings_form_candidate_data_enabled_set
    ewk_settings_text_selection_enabled_get
    ewk_settings_text_selection_enabled_set
    ewk_settings_text_autosizing_enabled_get
    ewk_settings_text_autosizing_enabled_set
    ewk_settings_uses_arrow_scroll_get
    ewk_settings_uses_arrow_scroll_set
    ewk_settings_clipboard_enabled_get
    ewk_settings_clipboard_enabled_set
    ewk_settings_ime_panel_enabled_get
    ewk_settings_ime_panel_enabled_set

Change-Id: I12b0dc4e362e7605e709941175a83397096c6ca6