Changes proposed in this pull request

• Install headers for generated CLib
• Exclude legacy CLib headers from installation when generated CLib is being used.

If applicable, fill in the issue number this pull request is fixing

Fixes (another) issue found while building conda-forge packages (see conda-forge/cantera-feedstock#63).

If applicable, provide an example illustrating new features this pull request is introducing

Checklist

• The pull request includes a clear description of this code change
• Commit messages have short titles and reference relevant issues
• Build passes (scons build & scons test) and unit tests address code coverage
• Style & formatting of contributed code follows contributing guidelines
• The pull request is ready for review