Small changes to logging configuration
Added some new PySide dialogs

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Complete overhaul of the PySide UI bundle

* Split main reactor into multiple reactors that handle specific widget
types
* TabManager overhauled. Works with any type of widget now instead of
just editors. Is a Python sequence.
* IOTask system introduced to run IO-bound tasks on background threads.
* Other, more minor changes and fixes
Change to how reactors are chosen

Reactors are now given more control over whether they are chosen to
react for a particular widget in the tab manager. Reactors now indicate
whether they are in control of a particular widget, rather than a type
of widget.
Updated UI and corelib bundles

* Added about dialog
* Added widget for rendering Jinja Templates inside the tabman
* Added widget for rendering reStructuredText inside the tabman
* Added widget for rendering basic HTML inside the tabman
* In corelib: added bundleutil package