Add warning for ambiguous library title

[JonnyWong16]

Description

Adds a warning for an ambiguous library title when retrieving library section. The last library section matching the name will be returned which is the same as the current behaviour when the lookup dictionary is clobbered.

>> python.library.section("Movies")
UserWarning: Multiple library sections with the same title found, use "sectionByID" instead. Returning the last section.

Fixes #1324

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the docstring for new or existing methods
• I have added tests when applicable