Improve test video recording

[dvojtise]

Companion PR of eclipse/gemoc-studio#190

This PR contributes a helper class that allows writing a log file that is aware of the start of the video recording.

In the Eclipse CI, the UI tests are now recorded in an mp4 video (ex: https://ci.eclipse.org/gemoc/job/gemoc-studio-integration/job/master/lastSuccessfulBuild/artifact/gemoc-studio/dev_support/full_compilation/target/)

This PR adds a log file in this folder with an indication of the time spent since the start of the video.

The language workbench and modelling tests contribute to this by adding a call to the helper class in the @beforeClass and the @setup

This produce logs such as:

2019-11-29 14:57:11+00:00
PT-1M-56.062S | Fri Nov 29 14:59:07 UTC 2019 | starting org.eclipse.gemoc.studio.tests.system.lwb.feature.XDSMLPerspective_Test
 PT-2M-5.139S | Fri Nov 29 14:59:16 UTC 2019 |    - test01_FileMenuContent
 PT-2M-9.384S | Fri Nov 29 14:59:20 UTC 2019 |    - test02_toolbarDropDownNewMenuContent
PT-2M-42.386S | Fri Nov 29 14:59:53 UTC 2019 |    - test03_toolbarContent
PT-2M-55.961S | Fri Nov 29 15:00:06 UTC 2019 | starting org.eclipse.gemoc.studio.tests.system.lwb.feature.GenerateTrace4OfficialExampleMelangeK3FSM_Test
 PT-3M-0.463S | Fri Nov 29 15:00:11 UTC 2019 |    - test01GenerateTrace_usingDirectCommand_NoErrorsInWorkspace
PT-4M-38.725S | Fri Nov 29 15:01:49 UTC 2019 | starting org.eclipse.gemoc.studio.tests.system.lwb.feature.GenerateLangRuntime4OfficialExampleMelangeK3FSM_Test
PT-6M-50.681S | Fri Nov 29 15:04:01 UTC 2019 | starting org.eclipse.gemoc.studio.tests.system.lwb.userstory.DeployOfficialExampleMelangeK3FSM_Test
PT-6M-53.949S | Fri Nov 29 15:04:04 UTC 2019 |    - test01_InstallMelangeK3Fsm
PT-7M-28.219S | Fri Nov 29 15:04:39 UTC 2019 | starting org.eclipse.gemoc.studio.tests.system.lwb.userstory.CreateSingleSequentialLanguageFromOfficialFSM_Test
PT-7M-43.247S | Fri Nov 29 15:04:54 UTC 2019 |    - test01_OpenXDSMLPerspective
PT-7M-48.577S | Fri Nov 29 15:04:59 UTC 2019 |    - test02_CreateSequentialLanguageProject
 PT-8M-9.652S | Fri Nov 29 15:05:20 UTC 2019 |    - test04_CreateTraceAddon
PT-8M-28.237S | Fri Nov 29 15:05:39 UTC 2019 |    - test05_CreateSiriusEditorForLanguage

where the first column indicates the duration since the beginning of the video

I hope it will help us debug the flaky tests (eclipse/gemoc-studio#123)