Adding image pagination

Add image pagination component so that multiple images can be cycled through without fetching them all. This is useful for loading analysis images for each template bank bin, for example, the horizon history and the background SNR_Chi^2 PDF from the ranking statistics.

Note: this should not cause any backward compatibility problem since it only adds new feature.

Demo: https://ldas-jobs.ligo.caltech.edu/~chiwai.chan/image_pagintation/

ligo/scald/report.py

@@ -294,6 +294,35 @@ class ImageGrid(Content):
         return self
 
 
+class ImagePagination(Content):
+    _type = 'image_pagination'
+
+    def __init__(self, title, footer=None, visible=True, **kwargs):
+        super(ImagePagination, self).__init__(**kwargs)
+        self.title = title
+        self.visible = visible
+        self.footer = footer
+        self.images = []
+
+        self.content.update({'title': self.title, 'images': self.images, 'visible': self.visible})
+        if self.footer:
+            self.content['footer'] = self.footer
+        self.content.update(kwargs)
+
+    def __iadd__(self, image):
+        self.images.append(image.content)
+        return self
+
+    def __len__(self):
+        return len(self.images)
+
+    def glob(self, glob_path):
+        for path in sorted(glob.glob(glob_path)):
+            self.images.append(Image(path=path).content)
+        self.images.sort(key = lambda x: x['path'])
+        return self
+
+
 class Table(Content):
     _type = 'table'
 
@@ -353,7 +382,7 @@ class Description(Content):
 
 def save_content(webdir, config):
     for content in config:
-        if 'image_grid' in content['name']:
+        if 'image_grid' in content['name'] or 'image_pagination' in content['name']:
             for image in content['images']:
                 if 'path' in image.keys():
                     shutil.copy2(image['path'], os.path.join(webdir, 'images'))