When saving a panel object, embed should be true by default

[Jacob-Barhak]

Look at the code at #672

To make the example be saved properly, there is a need to change the save line to:

p.save('test.html', embed=True)

The request is to make embed=True the default.

For simple use cases where a holoviews object is saved in panel, the regular use case is that the user expects that the html file will be functional.

If there are other reasons that prevent embed=True being a default, those should be raised as a warning if can be detected.

[Jacob-Barhak]

Moreover, safe embed #1040 should be true by default.

[Jacob-Barhak]

Also, it is important to indicate to the user if the generates save cannot faithfully represent the plot data and it is also important to document that the save freezes data and plots the snapshot in cases such as time dependent data.
Live data elements such as Dynamic Maps should be blocked from saving by raising an exception and making a user change a flag such as allow_dynamic_at_own_peril .
Using this flag should write a warning to the user that the generated plot may not accurately represent the data.