Added new experimental section that allows you to cut objects based on current clipping planes in the scene. The difference from other clipping plane methods - it actually (temporarily) edits meshes geometry and adds cappings at the cut. So, the clipped meshes can be seen both on render and cutted parts won't get in the way as they do with temporary section cutaways (shader based method)
Example - https://imgur.com/a/SOqovOM
bim.reassign_class wasn't considering that root.reassign_class will also reassign class for occurrences of the same type and was reaccessing invalid elements
The issue was related to the sheet names - Excel prohibits some symbols in the names and it doesn't allow sheet name to be longer than 31 symbols. If sheet names doesn't match this criteria then Excel says file appears to be corrupted - when file open data itself is not really corrupted besides the spreadsheet names that failed the criteria.
* initial ui
* changed the group name
* groups counter in ui
* added operators for selection and breaking link in the ui
* small removal
* changed IFC operators to _execute