Add low power mode

[leduythuccs]

This PR contains changes from #459. I created a different PR to clarify what each commit/PR does.

Description

Low power mode is a setting that helps us reduce DB/CPU usage by limiting what users can see.

What

• Limit pagination in low power mode: for the submission page, users are not allowed to view more than 5 pages.
• Only allow filtering by 1 submission result in low power mode:
  Production allows the status & language to be multi-select, which makes it very hard to index:

New changes also remove the org filter:

• Disable the submission pie chart in low power mode: yes, for the same reason as above.
• Avoid drawing heat map (the image below) for users with too many submissions, as of now only 1 users exceed 20k subs (vjudge1)