ENH: Add 'is_' method to Index for identity checks

Adds a method that can quickly tell whether something is a view or not
(in the way that actually matters).

Test cases and basic setup for is_ method

CLN: change 'is' check to 'is_' check in 'equals()'
BUG: Fix copy s.t. it always copies index/columns.

Only copies index/columns with `deep=True` on `BlockManager`. Plus some
tests...yay!

Change copy to make views of indices.

Requires changing groupby to check whether indices are identical, rather
than comparing with `is`. Plus add tests for name checks through
everything.

Add some views with data copying...

CLN: Change groupby to use 'is_' instead
ENH: enable deep copy for sparse Series/Panel