Issue #30: Whitelist gitignore

.gitignore

-# Created by .ignore support plugin (hsz.mobi)
-### Java template
-*.class
+# Ignore everything...
+*
 
-# Mobile Tools for Java (J2ME)
-.mtj.tmp/
+# ...except directories
+!*/
 
-# Package Files #
-*.jar
-*.war
-*.ear
+# ...and these files
+!*.java
+!.gitignore
+!README.md
+!pb162_codestyle.xml
+!polygon-error.txt
+!polygon-ok.txt
+!pom.xml
+!.gitlab-ci.yml
+# etc.
 
-# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
-hs_err_pid*
-### JetBrains template
-# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio
 
-*.iml
+# From directories, ignore...
 
-## Directory-based project format:
+### Idea:
 .idea/
-# if you remove the above rule, at least ignore the following:
-
-# User-specific stuff:
-# .idea/workspace.xml
-# .idea/tasks.xml
-# .idea/dictionaries
-
-# Sensitive or high-churn files:
-# .idea/dataSources.ids
-# .idea/dataSources.xml
-# .idea/sqlDataSources.xml
-# .idea/dynamic.xml
-# .idea/uiDesigner.xml
-
-# Gradle:
-# .idea/gradle.xml
-# .idea/libraries
-
-# Mongo Explorer plugin:
-# .idea/mongoSettings.xml
-
-## File-based project format:
-*.ipr
-*.iws
-
-## Plugin-specific files:
-
-# IntelliJ
-/out/
-
-# mpeltonen/sbt-idea plugin
 .idea_modules/
+/out/
 
-# JIRA plugin
-atlassian-ide-plugin.xml
-
-# Crashlytics plugin (for Android Studio and IntelliJ)
-com_crashlytics_export_strings.xml
-crashlytics.properties
-crashlytics-build.properties
 ### Maven template
 target/
-pom.xml.tag
-pom.xml.releaseBackup
-pom.xml.versionsBackup
-pom.xml.next
-release.properties
-dependency-reduced-pom.xml
-buildNumber.properties
-.mvn/timing.properties
+
 ### Eclipse template
-*.pydevproject
-.metadata
-.gradle
 bin/
 tmp/
-*.tmp
-*.bak
-*.swp
-*~.nib
-local.properties
 .settings/
-.loadpath
-
-# Eclipse Core
-.project
-
-# External tool builders
-.externalToolBuilders/
-
-# Locally stored "Eclipse launch configurations"
-*.launch
-
-# CDT-specific
-.cproject
-
-# JDT-specific (Eclipse Java Development Tools)
-.classpath
-
-# Java annotation processor (APT)
-.factorypath
-
-# PDT-specific
-.buildpath
-
-# sbteclipse plugin
-.target
-
-# TeXlipse plugin
-.texlipse
-### NetBeans template
-nbproject/private/
-build/
-nbbuild/
-dist/
-nbdist/
-nbactions.xml
-nb-configuration.xml
-.nb-gradle/
-
-# Vim
-*.un~
-
-# OS X .DS_Store
-.DS_Store
-
-# project files
-polygon-out.txt
-polygon.bin