Browser very slow to process board when high number of tasks

[2Belette]

Not really a bug but a behavior A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. having more than ~30/40 tasks total in the same board*
2. Adding / Editing a task / Removing a task
3. The browser/board needs about 20 sec to load!

I suspect a high number of object/JSON for the browser to process

Expected behavior The board update should be quicker to load

Please complete the following information:

• OS: Any (tested on Linux Hyperbola / ArchLinux / Windows 10)
• Browser [Firefox]
• Version [LTS 52.9 or other versions]