Fixed maven warnings about missing versions.

Version properties existed in the poms, they just weren't used. Used them.

```
[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.boundbox:boundbox-sample-integration-tests:jar:1.2.0
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 81, column 12
[WARNING] 'build.plugins.plugin.version' for org.codehaus.mojo:build-helper-maven-plugin is missing. @ line 63, column 12
[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.boundbox:boundbox-sample:jar:1.2.0
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 83, column 12
[WARNING] 'build.plugins.plugin.version' for org.codehaus.mojo:build-helper-maven-plugin is missing. @ line 65, column 12
[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.boundbox:boundbox-android-sample:apk:1.2.0
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 59, column 12
[WARNING]
[WARNING] Some problems were encountered while building the effective model for org.boundbox:boundbox-android-sample-tests:apk:1.2.0
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 96, column 12
[WARNING] 'build.plugins.plugin.version' for org.codehaus.mojo:build-helper-maven-plugin is missing. @ line 78, column 12
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
[WARNING]
```