Time Window selection

[stuckinforloop]

Description

Before starting a typing session, we should allow the user to change the default timer value (currently it's fixed to 30sec) similar to what other platforms like monkeytype provides.

User can select one of the following three values:

• 15 seconds
• 30 seconds
• 1 minute

For now, this can be done on the starting screen itself and later moved to a session config screen.