ENH: Add initial Viewer / view class

Works in Colab!

Addresses InsightSoftwareConsortium#99, more can be done with the window size.

Co-authored-by: Brianna Major <brianna.major@kitware.com>
Co-authored-by: Wei Ouyang <oeway007@gmail.com>

itkwidgets/view.py

@@ -0,0 +1,8 @@
+from .viewer import Viewer
+
+__all__ = [
+  "view",
+]
+
+def view(image=None):
+    return api.export(Viewer(image=image))

itkwidgets/viewer.py

@@ -0,0 +1,27 @@
+__all__ = [
+  "Viewer",
+]
+
+class Viewer:
+  """Viewer class."""
+
+  def __init__(self, **kwargs):
+      try:
+          from google.colab import output
+          self.running_in_colab = True
+      except ModuleNotFoundError:
+          self.running_in_colab = False
+      self.image = kwargs.get('image', None)
+
+  async def setup(self):
+      if self.running_in_colab:
+          viewer = await api.showDialog(
+              type='itk-vtk-viewer',
+              src='https://kitware.github.io/itk-vtk-viewer/app',
+          )
+      else:
+          viewer = await api.createWindow(
+              type='itk-vtk-viewer',
+              src='https://kitware.github.io/itk-vtk-viewer/app',
+          )
+      await viewer.setImage(self.image)