Added Optional Rules from DMG

[mfriik]

Added Optional Actions and Bonus Actions Climb onto a bigger creature - separate item in Actions Disarm - separate item in Actions Mark - separate item in Actions Overrun - separate item in Actions & Bonus Actions Shove Aside - Merged with Shove and added bullet points for this optional rule with a indication that this part is optional Tumble - separate item in Actions & Bonus Actions

Added new icons from game-icons.net and used a https://www.flaticon.com/free-icon/gymnast-somersault_20731 for tumble icon with modifications to image colors to alight with the game icons style.