Changed the names of the files to conform the python convection and also added photo_in_entry.py to diminish the cyclic import error in pylint

src/pilgrim/models/photo.py

@@ -0,0 +1,19 @@
+from sqlalchemy import Column, Integer, String
+from sqlalchemy.orm import relationship
+
+from pilgrim.models.photo_in_entry import photo_entry_association
+from ..database import Base
+
+
+class Photo(Base):
+    __tablename__ = "photo"
+    id = Column(Integer, primary_key=True)
+    filepath = Column(String)
+    name = Column(String)
+    addition_date = Column(String)
+    caption = Column(String)
+    entries = relationship(
+        "Entry",
+        secondary=photo_entry_association,
+        back_populates="photos"
+    )