updated documentation for CoreNodes/math
Second pass through CoreNodes documentation: removed redundant search tags
Documentation for CoreNodes/string
Forced ReExec refactorings

Update name of forced re-execution property, update the property  in the selection nodes, introduce added element watcher
reorganized startup logic
fixed uuid loading for selection nodes
Minimal multi-thread trace test
Move the test to outside the thread
Documentation for Python nodes
Documentation for DSOffice/Excel and revised searchTags for CoreNodes/Files
updates search tags for building sublists
addressed merge conflicts in src/Libraries/DSOffice/Excel.cs