Started reformulating the model.

This is for #234.
Removed unrequired public keyword
Fix for Dymola 2015 FD01 beta1 parameters

This changes the assignment of _T_a_start, _T_b_start and RTot to be in
the initial equation section as opposed to the parameter declaration.
This is needed to avoid an error during model check and translation in
Dymola 2015 FD01 beta1.
Improved documentation and expanded assignment.
Small editorial revisions
Moved declaration.

Moved declaration of compositeWall due to a bug in Dymola 2015 FD01
beta1.
Reverted replaceable change.

The replaceable keyword is needed in Dymola 2015 to allow assigning the
record from the GUI.
Added replaceable keyword.

This is need to assign data from the GUI through the pull down menu.
Avoided replaceable parameters

This simplifies the implementation by avoiding replaceable parameters
where they are not needed.
Changed assignment to use vector notation
Removed white spaces
Set start value to avoid conflicting start values.

Set start value for hPip(fluid(T)) to avoid
a warning about conflicting start values in Dymola 2015 FD01.
Removed invalid protected keyword.
Removed redundant connection
Removed access to conditional instance.
Added start value.

Set T(start=T_default) and p(start=p_default) in the
ThermodynamicState record. Setting the start value for
T is required to avoid an error due to conflicting start values
when checking
Buildings.Examples.VAVReheat.ClosedLoop in pedantic mode.
Removed compressibility of water and conflicting start values
Fix for issue 276

Reformulated solar collector model to allow using glycol.
Changed Cp_default to cp_default.
Removed unrequired instance system.
Changed medium to glycol.

This was done to have a unit test that uses glycol.
Merge pull request #277 from lbl-srg/issue276_collector

Issue276 collector