Additional wrappers for Tasks, Documents and Organization services

Additional wrappers for Tasks, Documents and Organization services

1. RequestExecutor
- added support for DELETE method

2.  Tasks
- added getTasks() by clientId, username, task status
- added deleteTask() by id

3. Organization
- additional methods to get lists of Branches and Centres with full
details (primarily needed to have addresses)

3. Documents (Demo only)
- added test to upload a document from a file
- added encoding helper method
- added test/data directory to place files for uploading

4.  DemoUtil
- moved some good patterns for getting demo data (found in Tasks) into
DemoUtil helper methods (getDemoUser() and getDemoClient())

5. test/data directory
- added 'data' under test (test/data) to place temp files for upload
testing