Move crash reporter info to utility.h
Setup exception handler around editor_t::perform

The implementation of kPaste seems to generate an exception for some users, but I don’t know exactly why, so this should provide some better diagnostics info.
Improve renaming files with hidden extension

We now clear the “hidden extension” flag if the user manually adds it.

We also ensure the hidden extension is not ignored by comparing base name with display name. The flag is ignored under certain circumstances.

Comparing base name with display name alone may give a false positive for localized file names.
Make fs::tree_t member data private
Don’t keep mutex locked longer than required