Did some refactor, add YouTube as search variant

bot/filters/__init__.py

@@ -0,0 +1 @@
+from .search import ServiceSearchFilter

bot/filters/search.py

@@ -0,0 +1,13 @@
+from aiogram.filters import BaseFilter
+from aiogram.types import InlineQuery
+
+
+class ServiceSearchFilter(BaseFilter):
+    def __init__(self, service_letter: str):
+        self.service_letter = f'{service_letter}:'
+
+    async def __call__(self, inline_query: InlineQuery):
+        return (
+                inline_query.query.startswith(self.service_letter) and
+                inline_query.query != self.service_letter
+        )