Support Modern OpenGL

[changh95]

Purpose

Refer to #22

Action

• Now supports GLAD and GLFW3 to use Modern OpenGL
• Also polished some pangolin related codes

Note

• Currrently running a full test... Will request for review when complete!
• Pangolin and GLAD will conflict when used together. This is because Pangolin loads GL related libraries internally which should only be loaded once, and GLAD will try to load them again. To avoid conflict, there must be #ifndef to avoid header duplication.
• I was logged into my work account when I made the commits :(