Add token size in project mode and in general token usage estimation

[ichts]

Based on the feedbacks on the subject of token limit/token usage from discord:

• show token usage for better UX and cost estimation: how token usage estimation in chat mode/vault QA/copilot plus/project mode
• Token limit/token size in project mode
  • Show the token limit for the selected model
  • when adding context (e.g. folder, tags etc.), the token used by each chunk of context should be also shown, so that the user can make sure that it doesn't surpass the model's limits without trial and error