add method and route to search across tracks, albums and artists.

+ break models into separate files
+ same for the utils and setup

app/models/folder.py

@@ -0,0 +1,10 @@
+from dataclasses import dataclass
+
+
+@dataclass(slots=True, frozen=True)
+class Folder:
+    name: str
+    path: str
+    has_tracks: bool
+    is_sym: bool = False
+    path_hash: str = ""