Add partialCopy() method for transferring well states.

Also add numWells() and numPhases() helpers.
Handle increasing numbers of active wells during simulation.

This uses partialCopy() to transfer the previous wells' data
to the new well state object.
Merge pull request #181 from atgeirr/num-wells-can-change

Allow number of wells to increase during simulation
Throw if elliptic solve fails.
Improve exception message, add (disabled) debugging helpers.
Fix saturation-change bug in updateState().
Fix output statements in run().

This fixes the following bugs:
 - No longer overwrite the matlab-output files each step.
 - Create output also for the initial state.
 - Change filenames of matlab-output by one (initial state is 000.txt,
   final state is NNN.txt and not (NNN-1).txt for total of NNN steps).
 - Eclipse binary output matches eclipse output (includes the same
   steps including initial state) for the same case.

Also added several comments outlining the parts of the run() function.
Merge pull request #182 from atgeirr/bugfix-updatestate

Bugfix for updateState()
Merge pull request #183 from atgeirr/fix-output

Fix output statements in SimulatorFullyImplicitBlackoil::run().