WOLF doc: Add a chapter with WOLF logic and algorithms

In particular, explain:

• Processor Motion API
• How the state & odometry of the robot is recovered (state_getter_ and state_priority_)
• How pre-integration works
• How keyframes are broadcasted
• How and why captures and frames are buffered in processors
• How trackers work
• How loop closers work
• How dynamic/static parameters are handled
• How to use libraries implementing front-ends in wolf processors
• How Tree managers work

assigned to @jsola

@joanvallve if you find more items to add to this list, please add them

changed the description

added Doing documentation labels

changed the description

marked the checklist item How pre-integration works as completed

marked the checklist item How and why captures and frames are buffered in processors as completed

marked the checklist item How trackers work as completed

marked the checklist item How loop closers work as completed

marked the checklist item Processor Motion API as completed

marked the checklist item How the state & odometry of the robot is recovered (state_getter_ and state_priority_) as completed

marked the checklist item How keyframes are broadcasted as completed

marked the checklist item How Tree managers work as completed

marked the checklist item How Tree managers work as incomplete