Add Warning When Setting burn-fee-cap and sats-per-bytes.

[gavinisagi]

Is your feature request related to a problem? Please describe.
Show a warning notification when

• 1. Setting burn-fee-cap and sats-per-bytes.
• 2. After click starting button.

Warning contains:

• 1. Shows how much will it burn every transaction.
• 2. How long will it last (compute by address they choose, 7 blocks per hour)
• 3. How much will it take for register key.