add 4-7-8 counter

[PacoSchwab]

Value proposition

As a user I want to be able to see a counter counting 4-7-8-seconds So that I know how long to inhale-hold breath-exhale

Description

Acceptance criteria

• [ ] a countdown is displayed, counting in three intervals: 4 -> 0 / -> 0 / 8 -> :
• [ ] after the three intervals the flow starts again in an infinite loop, tracking rounds
• [ ] the counter starts on click
• [ ] it stops on clicking again, displaying a success message

Tasks

• [ ] set counter states
• [ ] create a button
• [ ] display all counter intervals on the same button
• [ ] add a round tracker
• [ ] show success message on second button click