Optional ID for the tab, which can later be used to reference the tab. APIs requiring a reference to a tab will accept
the tabs ID [including
com.smartgwt.client.widgets.tab.TabSet#selectTab,
com.smartgwt.client.widgets.tab.TabSet#updateTab,
com.smartgwt.client.widgets.tab.TabSet#removeTab].
The ID will also be passed to the
com.smartgwt.client.widgets.tab.TabSet#addTabSelectedHandler and
com.smartgwt.client.widgets.tab.TabSet#addTabDeselectedHandler handler functions, if specified.
Note that if you provide an ID, it must be globally unique.