Maven/ant improvements (rebased onto dev_5_0)

This is the same as gh-2484 but rebased onto dev_5_0.

----

This combines:

 * https://github.com/openmicroscopy/openmicroscopy/pull/2372 (`dev_4_4` maven names, reviewed by @bpindelski) and
 * https://github.com/openmicroscopy/openmicroscopy/pull/2389 (`dev_5_0` ant versions, reviewed by @rleigh-dundee)

### Things that have changed ###
 * `ant` is now usable without `./build.py` from the top-level and each of the subcomponents.
 * Artifacts previously named, e.g., `5.1.0-DEV` are now named `5.1.1-SNAPSHOT`
 * Some jars are now downloaded and cached under `~/.m2/repository` in the Maven way.
 * `-javadoc` and `-sources` jars are now generated along with all regular jars.
 * The build is now slower. On my desktop, it has gone from 4 to 6 minutes, which is largely due to the more proactive generation of javadoc.

### Things that need to happen (possibly beyond this PR) ###
 * [ ] Setup a Maven job and push artifacts to artifactory (/cc @sbesson)
 * [ ] Migrate `pom-omero-client` and `minimal-omero-client` to http://github.com/ome
 * [ ] Enable some Maven-based testing on those repositories

### Testing ###
 * All build targets should continue to work normally.
 * Along with modifications to `~/.m2/settings.xml` (see sample below), it should be possibly to build https://github.com/joshmoore/pom-omero-client/tree/dev_5_0 with `mvn install`
 * Once `pom-omero-client` is built, it should be possible to build https://github.com/joshmoore/minimal-omero-client/tree/dev_5_0 with `mvn install` as well.
 * Development in Eclipse should be eased if following the pattern of `minimal-omero-client`.

### Sample `~/.m2/settings.xml` file for testing ###
```
<settings>
  <profiles>
    <profile>
      <id>ome</id>
      <repositories>
        <repository>
          <id>ome</id>
          <url>file:///opt/ome/target/repository</url>
          <releases><enabled>true</enabled></releases>
          <snapshots><enabled>true</enabled></snapshots>
        </repository>
      </repositories>
    </profile>
  </profiles>
  <activeProfiles>
    <activeProfile>ome</activeProfile>
  </activeProfiles>
</settings>
```