Implementing time derivatives for auxiliary variables (closes #442)

- The implementation adds another instance of TimeIntegrator class onto
  AuxiliarySystem.  So the code we already have to compute our time
  derivatives does not have to repeated.
- It removes coupled_dot_aux_var test, which was testing the case when
  somebody wanted to coupled u_dot of an aux-variable. We do not need
  the test since we added that capability.
- It fixes DotCouplingKernel which was missing a test function, but was
  used only in the removed test and thus it was not an real issue.
- It improves the documentation of TimeIntegrators and brings the
  references to the current, old and older solutions into the
  sub-system, thus resulting in a nicer code.
- It adds a new test to verify the functionality of newly added
  capability.

Known limitations:
- u_dot of an auxiliary variable cannot be used inside the auxiliary
  system, because in order to compute the time derivative, we have to
  compute the new state of the aux. variable. Thus, this computation is
  done after the update has happened.  All systems after auxiliary
  system can bring these new values and use them with no problems.
Remove deprecated yourFileName parameter in Piecewise closes #2421
Remove deprecated AdaptiveDT TimeStepper ref #2423
Merge pull request #3031 from bwspenc/deprecated

Remove deprecated yourFileName parameter in Piecewise
Merge pull request #3022 from andrsd/442

Implementing time derivatives for auxiliary variables (closes #442)
Merge pull request #3032 from bwspenc/deprecated_adaptive

Remove deprecated AdaptiveDT TimeStepper
turn no_solve test back on closes #1978
fix remaining issues with optional coupling refs #2358
Merge pull request #3034 from friedmud/no_solve_1978

turn no_solve test back on
Merge pull request #3035 from friedmud/optional_coupling_2358

fix remaining issues with optional coupling