Edera

* Upgraded the monitoring UI:
- Stopped failing when there are no snapshots available
- Added support for custom captions
- Made all anchors auto-focusing
- Added start/finish timestamps and the duration for completed tasks
- Added the full name of the task to facilitate search by name
- Started capturing important logs and publishing them in the UI
- Redesigned the UI a bit

* Got rid of the annoying animation flickering in monitoring UI
* Optimized `MongoStorage` by indexing it by (key, timestamp)

* Preserved tracebacks while reraising exceptions

* Handled None-targets during workflow testification

* Renamed (monitoring) `Server` to `App`
* Made relative URLs in the `App` WSGI-friendly

* Introduced infrastructure for workflow auto-testing:
- Use `TestableTask` to define tests and stubs for your tasks
- Use `WorkflowTestifier` to transform your workflows into auto-tests
- Use `TestingWorkflowExecuter` to run your testing workflows
- ...
- PROFIT!!!
* Fixed a major bug in `WorkflowNormalizer`
* Made a `Daemon` class out of the `daemon.run` function
* Got rid of `ManagedInvoker` and introduced `ManagedWorkflowExecuter`
* Generalized linearizers to any graphs and introduced `TaskRanker`
* Reworked the `Queue` class to go well with `TaskRanker`
* Introduced a new `annotate` requisite
* Added some syntactic sugar to `GraphNode`
* Enhanced `tox.ini`
* Improved task ordering in the "Edera Monitor" web-interface
* Changed the style of imports throughout the code
* Got rid of "private" modules
* Changed the style of the control panel in the "Edera Monitor" web-interface
* Fixed documentation