Remove unnecessary console logging

There should be no console logging in production
environment. Moreover such thing is an easy way
to memory leaks.
Replace collapse implementation

Leaflet provides utility function for DOM
manipulation so they should be used. This gives
more readable code.
Clean onAdd function

Previous code was a mess and had to be
refactored for better readability.
Moves control class name to constants

Class name was explicitly declared inside methods body. Such fields
should be declared as constants inside a class.