Feature configuration scene (depends on #10)

[CalvinMT]

Depends on #10 - Will rebase once #10 is merged

A configuration menu was added with the following configuration items:

• Sound state with options off, squelch, on
• Sensitivity with options from -127.0 to 0.0

Adding the configuration scene meant using one of the already used buttons. In this case, the left button was used as it is also used to open a configuration menu in other similar Flipper Zero applications. Buttons were updated as follows:

• UP: change scan direction to up
• DOWN: change scan direction to down
• LEFT: show configuration menu
• RIGHT: does nothing
• OK: changes scanning state

Finally, the main screen was updated for a clearer rendering:

• Sensitivty on same line as RSSI
• Scan direction (+/-) on same line as frequency
• Text alignement to the left
• Value alignement to the right

Fix #3
Fix #9