make it possible to activate highlighter only for specific file types

In stage 1 we use a glob pattern matching the file name.
Stage 2 (which I will maybe implement some day) might use some additional magic byte sequence for file type detection.

src/ui/bigtext/highlighting.py

@@ -25,6 +25,7 @@ class Highlighting:
             is_regex = session.getboolean(section, "is-regex", fallback=False)
             line_background_color = session.get(section, "line.background.color", fallback="None")
             hit_background_color = session.get(section, "hit.background.color", fallback="None")
+            activated_for_file_type = session.get(section, "activated-for-file-type", fallback="*")
 
             try:
                 highlight = HighlightRegex(
@@ -33,7 +34,8 @@ class Highlighting:
                     is_regex=is_regex,
                     hit_background_color=hit_background_color,
                     line_background_color=line_background_color,
-                    active=active
+                    active=active,
+                    activated_for_file_type=activated_for_file_type
                 )
                 result.append(highlight)
             except:
@@ -57,6 +59,7 @@ class Highlighting:
             settings.session.set(section, "is-regex", str(highlighter.is_regex))
             settings.session.set(section, "line.background.color", highlighter.line_background_color)
             settings.session.set(section, "hit.background.color", highlighter.hit_background_color)
+            settings.session.set(section, "activated-for-file-type", highlighter.activated_for_file_type)
 
     @staticmethod
     def remove_highlighting_sections(settings: Settings):