Feature/new thumbnails

[aaronchongth]

• reduced quality of OakTree and changed name (see below)

• changed thumbnail names to link to open source gazebo models:

  • OakTree -> oak_tree
  • PineTree -> pine_tree
  • CafeTable -> cafe_table
  • Fountain -> fountain
  • StandingPerson -> person_standing
  • Postbox -> postbox

• added new thumbnails:

  • Table
  • ambulance
  • beer
  • cafe
  • construction_barrel
  • construction_cone
  • gazebo
  • lamp_post
  • playground
  • suv

I don't think the thumbnails that have their names changed will affect any of our existing worlds. There is the dilemma that even though we are supporting the open source models, some of them don't follow our CamelCase naming conventions, which makes the list of thumbnail names not uniform. Let me know what your thoughts are.

[codebot]

Yeah, there are Gazebo/Ignition models all over that have various CamelCase or snake_case conventions. I don't think we can enforce either one, so let's just use whatever the upstream model is using.