Made OpenCV optional with "[VIZ]" extra. According to Issue #14

Author: TimoK93

README.md

@@ -52,6 +52,12 @@ cd py-ctcmetrics
 pip install .
 ```
 
+**Note**: If you want to use the visualization feature, you need to install OpenCV or by installing the optional dependencies:
+```bash
+pip install py-ctcmetrics[viz]
+```
+
+
 ---
 
 ## Usage

setup.py

@@ -2,17 +2,19 @@
 
 setup(
     name="py-ctcmetrics",
-    version="1.1.0",
+    version="1.2.0",
     packages=find_packages(),
     install_requires=[
         "numpy",
-        "opencv-python",
         "scikit-learn",
         "scipy",
         "tifffile",
         "imagecodecs",
         "pandas"
     ],
+    extras_require={
+        "viz": ["opencv-python"],
+    },
     author="Timo Kaiser",
     author_email="kaiser@tnt.uni-hannover.de",
     description="Metrics for Cell Tracking Challenges",