Log the stack trace when a LoadingQueue task throws an error

Fixes #658.
Merge pull request #659 from peitschie/log-fixup

Log the stack trace when a LoadingQueue task throws an error
Attempt to read selection style information even when there
is no text element/node in the selection.
Generate and cache style summary for selections that do not
contain text.

This divides the `isEnabled` information of DirectFormattingController
into two parts, `directTextStyling` and `directParagraphStyling`.

The widgets are accordingly updated.
Rename isEnabled to enabledFeatures inside DirectFormattingController.
Merge pull request #660 from adityab/annotation-selection-style

Fix style buttons' behavior when selecting the two positions around an annotation
Split Editor into Wodo.Texteditor and Wodo.CollabTexteditor
move fullscreen pinch-zoom into own class FullWindowZoomHelper
add product wodotexteditor
Add HOWTO-wodotexteditor.md
Add README.md to programs/editor
Create API dox for Wodo.TextEditor
Improvements to the usage sample files

fixups, to be squashed
keep backend for collabsession demo conifgurable, instead of hardcoding pullbox

fixup
more fixups to be sqashed