Refactor Dialogue system

Once Dialogue system is finished, a refactor to rename scripts, comment code, and clean up according to a more uniform design philosophy.

Dialogue.cs, for example, could be renamed "DialogueManager.cs" or "DialogueEngine.cs". with functions to load text more clearly marked inside as well as reducing duplicate code. Consider separate classes?

Start by reading Dialogue.cs and reviewing how the Dialogue system currently loads text and duplicates code. The issue proposes renaming the script, clarifying function organization, adding comments, and possibly separating classes; completion criteria and the intended design should be clarified before work begins.

Written by the indexing model from the issue text.