Improve flagging for high rejection submitters

[coffee2code]

The auto-flagging system currently flags when a submitter has a high number of rejections. This is displayed as a red or orange flag "Has rejections (N)" where N is the number of rejections. However, it is not apparent (and is rather a bit misleading) that the flag isn't based purely on the number of rejections or that there are rejections at all, but that it's their number of rejections relative to their number of published photos.

I propose clarifying the wording of the flags, improving the number it presents, and adjusting the wording based on how severe the rejection rate is for the user. Additionally, the criteria for flagging should be tweaked slightly.

These changes should consist of:

• If there are more rejections than approvals, create a new red flag "More Rejections Than Approvals"
• For all flags that follow below, N should be the rejection rate percentage for the submitter round( (rejections / ( rejections + published )) * 100, 0)
• Create a new critical threshold of 0.50 and if met, then show a red flag "Very High Rejection Rate (N%)"
• Adjust the existing alert threshold from 0.25 to 0.30 and display as an orange flag "High Rejection Rate (N%)"
• Adjust the existing warning threshold from 0.10 to 0.15 and display as a yellowish flag "Rejection Rate (N%)"

[coffee2code]

In 12959:

Photo Directory, Moderation: Improve flagging of high rejection users.

• Reword flag text to better reflect that it's based on a percentage of rejections against total submissions
• Increase flagging thresholds to 0.15 and 0.3 for warnings and alerts, respectively
• Add new critical threshold of 0.5
• Change how the rejection percentage is calculated
• Add new "More rejections than approvals" flag
• Change colors used for 'likely' and 'possible' flags

Fixes #7335.