Get XMP metadata from image using Pillow. Remove ExifTool dependency

- Pillow already supports reading XMP metadata from Images
- Removes need to maintain my fork of unmaintained PyExiftool
  - This also removes dependency on system Exiftool package for
    XMP metadata extraction
- Add test to verify XMP metadata extracted from test images
- Remove references to Exiftool from Documentation

Dockerfile

@@ -4,7 +4,7 @@ LABEL org.opencontainers.image.source https://github.com/debanjum/khoj
 
 # Install System Dependencies
 RUN apt-get update -y && \
-    apt-get -y install libimage-exiftool-perl python3-pyqt5
+    apt-get -y install python3-pyqt5
 
 # Copy Application to Container
 COPY . /app