Fix build release (metafacture#397)

Add gradle.properties to gitignore:
The gradle.properties is used when doing releases. Doing releases is only possible
with a clean git repo. Adding gradle.properties to gitignore provides both.

Add "developers" into pom:
The nexus repository manager insists on having the developers section in the pom.
This commit reverts parts of 8710014 to have the
developers section again.

.gitignore

@@ -48,3 +48,5 @@ buildbot.keyring
 # Ignore VS code/codium config files
 .vscode
 
+# Ignore files with sensitive data
+gradle.properties

build.gradle

@@ -143,6 +143,28 @@ gradle.projectsEvaluated {
       }
       url 'https://github.com/metafacture/metafacture-core'
       inceptionYear '2011'
+      developers {
+        developer {
+          id 'mgeipel'
+          name 'Markus M. Geipel'
+          email '[email protected]'
+          url 'https://github.com/mgeipel'
+          roles {
+            role 'architect'
+            role 'developer'
+          }
+        }
+        developer {
+          id 'cboehme'
+          name 'Christoph Böhme'
+          email '[email protected]'
+          url 'https://github.com/cboehme'
+          roles {
+            role 'architect'
+            role 'developer'
+          }
+        }
+      }
       organization {
         name 'Metafacture'
         url 'https://github.com/metafacture'