Convert to a multi-module Maven setup

This is much more user-friendly - users can either compile a specific module or create a profile to compile for the specific Minecraft versions they're looking to support. It means that it's much easier for people to continue assisting with the development of OpenInv in the future without access to every version of CB since 1.4.5.

This commit restores and updates most of the old system.

plugin/pom.xml

@@ -0,0 +1,38 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>com.lishid</groupId>
+    <artifactId>openinv</artifactId>
+    <version>1.0-SNAPSHOT</version>
+  </parent>
+
+  <artifactId>openinvplugin</artifactId>
+  <name>OpenInvPlugin</name>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.bukkit</groupId>
+      <artifactId>bukkit</artifactId>
+      <!-- Really should use 1.4.5-R1.0, but the InventoryDragEvent doesn't exist. TODO separate module? -->
+      <version>1.11-R0.1-SNAPSHOT</version>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.lishid</groupId>
+      <artifactId>openinvinternal</artifactId>
+      <version>1.0-SNAPSHOT</version>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <resources>
+      <resource>
+        <directory>src/main/resources</directory>
+        <filtering>true</filtering>
+      </resource>
+    </resources>
+  </build>
+
+</project>