Add DanglingLine boundary side P, Q, Vmag, Vangle

[jeandemanged]

Please check if the PR fulfills these requirements

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

Does this PR already have an issue describing the problem?

No

What kind of change does this PR introduce?

Feature

What is the current behavior?

We don't have access to DanglingLine results at boundary side

What is the new behavior (if this is a feature change)? Network.get_dangling_lines() new (optional) columns:

• boundary_p
• boundary_q
• boundary_v_mag
• boundary_v_angle

Does this PR introduce a breaking change or deprecate an API?

• [x] No