Fix support for using xTensor instead of TensorTools
Make output quieter when using xTensor
Remove unneded code from xTensor example
Add commented out code showing how to enable xTensor support
Use xTensor by default
Make sure xAct packages make it onto the $ContextPath

Also improve usage messages.
Rework xTensor interface

This new version should be much more robust and easier to use.
Rework EM-xTensor example to use the new xTensor interface
Make TensorTools style indices work with xTensor interface
Add Euc and Eps tensors when xTensor is used
Regenerate EM example with master branch commit eca6928f0542a28dcfad3dbc2bb3fec69a128cd6
Make sure error messages are created when using xTensor
Remove useless info message
Remove unnecessary code
Add fixme
Remove TensorTools

It's too confusing having it around at the same time as xTensor.
Rename Group symbol as it conflicts with a similar symbol in xAct
Rename Scalar symbol as it conflicts with a similar symbol in xAct
Only use characters for indices which aren't used elsewhere
Disable SetEnhancedTimes for EM-xTensor example