enable localization of gwt resources

Run:
```
mvn process-test-resources -Dgwt-i18n
```
will generate properties files (default locale as well as translation skeleton files) from those java interfaces and copy them to correct location
```
mvn zanata:push -Dzanata.pushType=both
```
will push generated files to zanata.org. We rely on merge type AUTO so that new generated translation skeleton won't override existing translation on server. 

see https://translate.zanata.org/zanata/iteration/view/zanata-editor/master