Seperate open and load functionality

[phillmac]

Problem

In the current implementation the database manager .get() method handles both load and open functions.
This isn't ideal because:

• Increases the difficulty of implementing new features
• Non-intuitive behaviour - HTTP GET requests to the api will actually attempt to open the database that are not already opened rather than throw an error. HTTP standards discourage GET requests having side effects, the api should be designed to use POST instead.

Solution

1. Separately implement .load(), and remove loading functionality from .get()
2. Modify api routes to use the appropriate manager methods

Resultant breaking api changes

• GET /db routes with a would instead throw a HTTP 40X error if the database is not opened
• POST /db would throw a 400 error if a database is already opened