refactor(grunt): add livereload to the maven command

https://github.com/camunda/camunda-bpm-webapp/commit/01930d89621165f72ae31e2c31467408fca9c2d0#diff-04c6e90faac2675aa89e2176d2eec7d8R123
refactor(grunt): add the -o (offline) flag for mvn process