Coordinate state variable names fixes #135

Address issue #135 and give the coordinate state variable suitable names. These are currently "value" and "speed". The full names are "<coordinateName>/value"  and "<coordinateName>/speed". This change re-exposed numerous frailties in how OpenSim establishes correspondence between values in files and state variables belonging to Components and the underlying State.  These include having multiple places were this "correspondence" is being established (e.g. `Model::fromCompleteStorage()`, `SimbodyEngine::formCompleteStorages()`, and `CMC_TaskSet::setFunctions()` to name a few. Other issues include performing the look-up within a computational method, e.g. `StaticOptimizationTarget::computeConstraintVector()` that is called thousands of times during an optimization. These should be addressed by future PRs.
>What exactly is this? Is this the full name of the state variable for the coordinate's speed? If so, could the comment say this?

It is the name of the coordinate's state variable corresponding to its speed. It replaces the <coordinate_name>_u convention with <coordinate_name>/speed.  

I will add a comment for the time being, but my long term plan is to eliminate it. The Coordinate should not be treated any differently than any other Component with state variables. Asking for and accessing the values by <state_variable_name> should be used universally. This will remove some of the hacks in CMC_Task, SO etc...