move abr import to main menu, add progress bar

src/brush.cpp

@@ -323,7 +323,7 @@ bool Brush::load_pattern(const std::string& path, const std::string& thumb)
     m_pattern_texture->create_mipmaps();
     m_pattern_texture->auto_destroy = true;
     m_pattern_path = path;
-    m_texture_thumb_path = thumb;
+    m_pattern_thumb_path = thumb;
     return true;
 }