537208: Task data filename can get too long

* moved file-related operations to a separate class
* file name is only encoded if required
* file name is trimmed to stay below 255 characters
* encoded file name always used if file already exists
* added unit tests for file-related methods

Change-Id: I8b536b3a3df8168b997aa9be1ec82b9f7e314dfd
Task-Url: https://bugs.eclipse.org/bugs/show_bug.cgi?id=537208
Signed-off-by: alexei.trebounskikh <alexei.trebounskikh@tasktop.com>
3 files changed