Move `token.hpp` and `token.cpp` into `lib` folder
Also moved the class from the `se2::fsm` namespace to `se2`.
Move empty functions of `state` from cpp to header
Add `token_mgr` class
This class manages all tokens in the system.
Modify `isr` and `dispatcher` to listen only on falling edges
An exception for this rule are `EVENT_SENSOR_HEIGHT`,
`EVENT_SENSOR_SLIDE` and `EVENT_SENSOR_EXIT`. There are new events to
listen on for the rising edges. For rising edge use the following
enumeration literals: `EVENT_SENSOR_HEIGHT_R`, `EVENT_SENSOR_SLIDE_R`,
`EVENT_SENSOR_EXIT_R`.