web: Display activity overlay when triggering from other sources (#84)
web: Improve download-handling (#82)

- Set correct Content-length in HTTP response
- Display activity overlay until the content length has been determined
web: Display help text when no workflows are present (#79)
web: Open lightbox images in new tab/window on click (#85)
web: Improve alert messages handling (#77, #78)

- Only the last 3 message are shown as alerts at the top of the screen
- A red label next to the log-button indicates how many errors/warnings
  are yet unread
- Clicking on any part of the message closes it now
web: Implement nicer URLs via HTML5 pushState; Changed API endpoints
web: Serialize datetime objects as epoch timestamps with microsecond
precision to avoid accidentally duplicated keys
web: Bring back 'finish capture' button (#79)
web: Use HTML form-element for forms (#83)
web: Update window title for each component
web: Remove unused code
web: Add warning not to remove workflows that are being downloaded (#75)
web: Update JavaScript bundles