Create consistent formatting for all examples in the gallery

[moorepants]

Here is a suggestion:

Title
=====

.. note:: installation note

Objectives
----------

Introduction
------------

Other headings as needed
------------------------

The objectives section would list the purpose and unique aspects of the example.

I basically have this in the park2004 example: https://opty.readthedocs.io/latest/examples/advanced/plot_park2004.html

We should also try to consistently use the mathematical notation in the theory page. I also tried this in the park 2004 example.

• plot_ball_rolling_on_spinning_disc.py
• plot_car_around_pylons.py
• plot_car_in_garage.py
• plot_human_gait.py
• plot_one_legged_time_trial.py
• plot_park2004.py
• plot_particle_in_tube.py
• plot_sit_to_stand.py
• plot_betts_10_103_104.py
• plot_betts_10_50.py
• plot_betts_10_7.py
• plot_betts2003.py
• plot_pendulum_swing_up_fixed_duration.py
• plot_pendulum_swing_up_variable_duration.py
• plot_sliding_block.py
• plot_vyasarayani.py
• plot_countersteer.py
• plot_crane_moving_a_load.py
• plot_drone.py
• plot_mississippi_steamboat.py
• plot_non_contiguous_parameter_identification.py
• plot_parallel_park.py
• plot_two_link_pendulum_on_a_cart.py