Indicate on config page if the extension file can be loaded

Problem/Motivation

The config page doesn't indicate if the sqlite extension can be loaded.

Proposed resolution

Add an indication on the sqlite configuration page on whether the extension can be loaded.
Maybe also add hook_requirements() to indicate the same thing.

Remaining tasks

Add an indication on the sqlite configuration page on whether the extension can be loaded.

User interface changes

The configuration page indicates if the extension is loadable.

API changes

TBD

Data model changes

TBD