Allow to add idler even if adaptor paused

Allow to add idler even if adaptor paused

Let we install idler function even if Adaptor is paused.

Since the Adaptor pause state depend on by Windows visibility, not app state,
Application::AddIdle() API usage make some confused.

For example, We cannot call AddIdle() at Application::OnResume callback
because the Window::OnIconifyChanged signal still not comed.

To avoid it, let we just allow Idler function add even Adator is paused.

Change-Id: I943ef76d4e759e282675fbcbc06f0a87d95e9fea
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>