Add feature to add instrument types

[ssaamm]

Includes:

• Add instrument type
• List instrument types
• Add reading of a specific instrument
• Show readings of a specific instrument

[ssaamm]

We said we'd do this in the conceptual design report. I personally think this is a janky way to do this. Users' actions shouldn't result in a new table being created.

This code is vulnerable to SQL injection. As far as I can tell, the PDO API doesn't have a way to escape user input in table creation statements (most likely because user input shouldn't be in table creation statements).

[ssaamm]

We decided this was dumb.