DOC: Add only latex notes for examples with GIF animation

[SMoraisAnsys]

Some examples can't be included in the PDF files as they contain animated GIF.
We should remove them from the PDF files and add a note stating that users can get this example through online documentation.
For example:

.. only:: latex

    Examples ... contain animated GIF.
    `View online <TBD>`_ if you are reading the PDF version of this documentation.

Currently concerned examples : "Maxwell2D_Transient.py", "Maxwell2D_DCConduction.py" and "Hfss_Icepak_Coupling.py"
See #67