Catch synchronous exceptions in request handlers
Unconditionally create / upgrade system tables on startup

There is no point in checking whether the table exists, as this is now handled
in the table creation code. This makes sure that full schema checking is done
every time. (Well, once https://phabricator.wikimedia.org/T75808) is done.
Fix / temporarily silence JSHint issues in proxyHandler

This code is not used yet, and would likely not work anyway. It currently
breaks JSHint in general, so silence it by fixing / working around the issues
for now.
Release restbase v0.2.5

Also bump the restbase-cassandra dependency to 0.2.5
Add a nicer request flow diagram

Replace the old ASCII art with a nicer SVG request flow diagram.
Merge pull request #34 from gwicke/doc_images

Add images in docs