Uniformity of joints specific properties

[Gregwar]

As discussed in 104, we currently have several properties that can be set for joints:

• The inv, set with a keyword in the dof name,
• The continuous/whell also set with keyword,
• The joint limits sets with jointMaxEffort and jointMaxEffort

This could be uniformized in config.json under one entry, like:

{
  "joints": {
    "wheel": {
        "invert": true,
        "continuous": true
        "speed_limit": 4
     }
  }
}

ping @DevnathNair