Marking episodes-played in bulk is slow

[amugofjava]

Describe the bug The 'Mark all episodes as read' option is very slow at updating the episodes. It also appears to get slower the more you do.

To Reproduce Steps to reproduce the behavior:

1. Start following podcasts.
2. Mark all episodes as read
3. Process gets increasingly slower.

Expected behavior Updating the episodes should be quicker and should not get progressively slower.

Smartphone (please complete the following information):

• Device: Google Nexus 5
• OS: Android 6