Issue/project clean should lock workspace 1001658

We need to lock the whole workspace when cleaning a project. Please, read the commit messages for details.

[As explained in the related ticket](https://scala-ide-portfolio.assembla.com/spaces/scala-ide/tickets/1001658?comment=292921533#comment:292921533), this issue only happens in master and it does not need to be backported. To prove it, I could backport only the commit that adds the test (i.e., ac97f1bf18633aaf725ec6477390d8a9c3def9d4). Should I do so?