change KPIs order and text

[PTiagorio]

We should change how we present our KPIs, starting with the most important and ending with the least. Suggested order:

• Models Users Per Month (and the title should change to "Models' Usage per Month");
• Users per Month;
• Active Users per Month;
• $U per Month;
• Retention Rate Month by Month - Acc;
• New Users per Month;

Besides, all the titles of the charts with the words "Per" and "By" should be changed to "per" and "by", respectively.