Move digger-web tasks to digger

This allows digger-web to be a real GUI application, without relying on
a hack to hide the console window as soon as it's created.
Improve rev parsing
Rename digger-web directory to web

The old name was conflicting with digger-web.d
(e.g. when running rdmd --build-only digger-web.d).
Trigger initialization from JavaScript

This prevents the "Browse to <url>" message from scrolling off-screen
prematurely.
webtasks: Add enforce messages
ae.sys.d.build: Cleanup
ae.sys.d.build: Move build ID calculation to DBuilder
digger: Fix return code propagation

Regression introduced in 6deac9f2add3f0374899afa31e51a818f409a493