Improve error handling across the code base

[vedxyz]

In order to iterate quickly while being developed as a proof of concept, most error handling was completely skipped. While the app can work for the most part without errors, it certainly needs to be much more resilient.

Some pain points off the top of my head are:

• Login sequence does not check errors, probably fails hard with any incorrect steps
• Session timeout is not checked for at all
• The existence of an internet connection is not checked