Support fragment and dialog

Issue #138 
Issue #294 
Fragment can be passed in instead of activity
Dialog can be used as well
Webview is hosted inside the dialog, which is created by ADAL. Developer can customize layout file for this dialog. Webview component is not customizable. 
Sample app is updated for dialog example.
IWindowComponent is exposed to define different types of fragments.
I could not change this in current version. If developers already included this layout to customize,  it will break their code.