Implement SQL Backend

[chatziiola]

At this moment in time the only bottleneck in the package is the fact that, since it limits itself to file operations, it takes some time to open all lecture files in buffers and get the information required to open them.

This becomes obvious when comparing the time between the first time you call the driver function and the second time. In the second time (since all lecture files have already been opened in buffers), the prompt appears almost instantly.

One way to deal with this problem, and this is 100% inspired by org-roam, would be to have some database backend, from which I could read the data**

** While writing this i thought that a simple plain-text should suffice, if properly manipulated and standardized