Add ID to encodings

[cyrusae]

• reader.ts should check for and return the current largest ID in table Encodings while it's there (if one exists; return 0 if not)
• Statement display should initialize with a counter equal to whatever that is
• On selection of a new highlight, id='[that count + 1]' should be added to its produced code, and the count should increment

Backwards-compatibility isn't a huge issue due to #74; in turn, this is an attempt at reaching forwards to the point where the HTML is just straight up dynamically generated instead of saved in the database.