Terminology selection and consistency

[devmount]

Describe the bug
It would be a great improvement to use more common/familiar/canonical mail terms. Examples:

• Daytime / By Hour / Hourly
• emails / mails / messages
• Received from / Sender
• Sent to / Recipient
• Flagged / Tagged / Starred
• Temporal distribution / Hourly
• ...

A common and consistent language/dictionary of terms will improve usability and understanding, and complement visualization mechanics and dimension-specific functionality. What's the minimal set of terms possible?

• Identify key terms
• Match key terms with those, Thunderbird already uses
• Decide which term to use
• Update ThirdStats UI
• Adapt other languages

Additional context
#376 (comment)