Fix escape sequence usage in strings. Remove unneeded import of os

Rename /config API method to config to match it's purpose. UI is
anyway too generic, and not what it is doing

src/processor/org_mode/orgnode.py

@@ -194,7 +194,7 @@ def makelist(filename):
           n.setHeading(prtysrch.group(2))
 
        # Set SOURCE property to a file+heading based org-mode link to the entry
-       escaped_heading = n.Heading().replace("[","\[").replace("]","\]")
+       escaped_heading = n.Heading().replace("[","\\[").replace("]","\\]")
        n.properties['SOURCE'] = f'[[file:{normalize_filename(filename)}::*{escaped_heading}]]'
 
    return nodelist