cleanup code into a separate DateParser class;

remove modified date from exif candidate fields;
add filename date parsing;
choose earliest among EXIF fields, dateTaken, mtime, filename without priority to any one;
add tests for DateParser;

Author: difanta

android/app/build.gradle

@@ -34,6 +34,19 @@ android {
     buildFeatures {
         viewBinding true
     }
+
+    testOptions {
+        unitTests.all {
+            useJUnitPlatform()
+
+            testLogging {
+                events "skipped", "failed"
+                showStandardStreams = true
+                exceptionFormat = "full"
+            }
+        }
+        unitTests.returnDefaultValues = true
+    }
 }
 
 dependencies {