Add a 2D rigid body component

[kianmolani]

This issue will focus on creating a 1D or 2D rigid body line or box. Said rigid body will initially be constructed in a 2D absolute reference frame / world environment. The component will at least possess the following parameters: s_start, s_end, w (initial angular velocity), a (initial angular acceleration), and m (mass) or rho (density). The parameters s_start and s_end are two points, and a vector will be drawn between them, thereby defining the spatial extents of our rigid body. This "two-point" vector implementation differs from Modelica's implementation of the same component. In the Modelica implementation, one point is used to define the position of the origin of a new frame of reference, and a second point is used to create a vector from the origin of this new frame. Having components possess their own reference frames in this way presents a series of advantages, but for now I will keep my implementation as simple as possible.