toggle breathing exercises

[PacoSchwab]

Value proposition

As a user I want to be able to switch between focused an power breathing So that I can choose the desired exercise without leaving the page

Description

Acceptance criteria

• [x] the focused and power breathing page are merged into one single page (former focused breathing page)
• [x] a toggle buttons switches between focused and power breathing
• [x] the remaining page is deleted

Tasks

• [x] add a toggle button
• [x] clicking the button changes breath interval delay
• [x] delete remaining page

[ella-blaupause]

LGTM✅