Support for a "watch" parameter for uploads + misc. build improvments

* Support for the "watch" flag was missing from the upload code. I added a boolean parameter to MWApi.upload while keeping the previous method signature with a sensible default. API compatibility is not broken and default behavior mimics previous versions.
* Changed the source and target version to Java 6 in pom.xml, which was left to 1.5 but didn't compile with JDK 1.5.
* Moved the test case to standard directory src/test/java
* Added the Maven failsafe plugin for integration testing (see https://maven.apache.org/surefire/maven-failsafe-plugin/) and accordingly renamed the test case to MWApiIT as it requires a running Mediawiki server. IT tests may be skipped with -DskipITs=true.