What's this "spacer" lever on the front brake lever for?
Adding pictures to Weiwen's answer...

Here is a picture of a brake lever with the part in question circled in blue.



It is a quick release mechanism integrated into the brake lever that allows increasing the space between the brake pad and the rim for easy wheel removal. Flipping the lever to the right or left in effect makes the brake cable longer allowing the brake pads to open wider.

Other ways a brake quick release has been implemented...

This brake lever has a quick release button


Sometimes the quick release mechanism is located in the brake caliper.


Sometimes it is located in the brake cable hanger/stop, in this case the front cable hanger


On a side note - is that speaker wire used to power the lamp?