feat: Multiplayer (#2)

Make this game multiplayer.

Setup:
- `common` for common classes used both by the server and the client
- `game` the actual client
- `server` the server

Reviewed-on: https://gitea.local.jzitnik.dev/jzitnik/game/pulls/2
Co-authored-by: jzitnik-dev <email@jzitnik.dev>
Co-committed-by: jzitnik-dev <email@jzitnik.dev>

server/.gitignore

@@ -0,0 +1,39 @@
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+.kotlin
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store