Helper function to set component data

[chapulina]

Addresses #84 .

Adds the SetComponentData function, which simplifies the code necessary to set data to a component that may not be created yet.

It simplifies code like this:

auto poseComp = _ecm.Component<components::Pose>(entity); 
if (nullptr == poseComp) 
{ 
  _ecm.CreateComponent(entity, components::Pose({force})); 
} 
else 
{ 
  poseComp->SetData(pose,
      [](const math::Pose3d &_a, const math::Pose3d &_b)
      {
        return _a == _b;
      };);
} 

Into:

ecm.SetComponentData<components::Pose>(entity, pose);

[mjcarroll]

This looks good, but will need to pass CI, it isn't currently getting past codecheck.

[codecov]

Codecov Report

Merging #436 (af4100c) into ign-gazebo3 (990e4f2) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           ign-gazebo3     #436      +/-   ##
===============================================
+ Coverage        77.31%   77.33%   +0.02%     
===============================================
  Files              205      205              
  Lines            11018    11028      +10     
===============================================
+ Hits              8519     8529      +10     
  Misses            2499     2499              

Impacted Files	Coverage Δ
include/ignition/gazebo/EntityComponentManager.hh	100.00% <ø> (ø)
include/ignition/gazebo/components/Component.hh	100.00% <ø> (ø)
...e/ignition/gazebo/detail/EntityComponentManager.hh	95.00% <100.00%> (+0.38%)	⬆️

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[diegoferigo]

xref #325