Atomic: Implementation of IonBuilder and circular polarization support

[yhteoh]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  bug fix and feature

• What is the current behavior? (You can also link to an open issue here)

• Complex values not supported for polarization of beam (Allow Complex Input for Wavevector Definition of Beams #64)
• No shortcut for building Ions

• What is the new behavior (if this is a feature change)?

• Support for complex polarization vector
• Builders for building commonly used ions
  • Yb171+
  • Ba133+
• Build reduced Ion and allow exclusions
• Zeeman shift calculations during build

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  No

• Other information:
  This pull request includes the changes from [feat] IonBuilder  #57

[benjimaclellan]

Looks good!

[benjimaclellan]

What does the II stand for in the builder name?

[yhteoh]

A way to note it's an singly ionized ion, the NIST database uses this notation