replace NameMap in aiger_reader by names_view.

[hriener]

The PR replaces NameMap in aiger_reader by names_view (addresses issue #218).

[coveralls]

Pull Request Test Coverage Report for Build 665872093

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.1%) to 80.17%

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Files with Coverage Reduction	New Missed Lines	%
include/mockturtle/views/names_view.hpp	2	93.75%
include/mockturtle/algorithms/dsd_decomposition.hpp	3	87.32%

Totals
Change from base Build 654610522:	0.1%
Covered Lines:	10661
Relevant Lines:	13298

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💛 - Coveralls