Updated to support Mambu 3.6

1. Added new services to support new 3.6 APIs:
1.1 MBU-5477 -As a Developer, I'd like to lock & unlock loans via API
(LoanService)
1.2 MBU-5476 -As a Developer, I'd like to apply arbitrary fees to
deposit account via API
(SavingsService)
1.3  MBU-5084- As a Developer, I'd like to get attachments via API
The following services now support getting a list of attached documents:
Clients, Groups, Loans and Savings
DocumentsService now also supports retrieving a specific document by
its ID.
1.4  Updated Maven Pom file to use 3.6 model.jar and to build
Mambu-Apis-Java-3.6-bin.jar

Note: 3.6-model.jar was built with Java 7. So Java 7 development
environment might be required to modify and build the latest wrappers
code.

Applicable Services and DemoTest programs were updated accordingly

2. Changes:
2.1  MBU-5278 - Update API calls are not individually mapped per each
component.
Modified Update APIs accordingly. The following 'entity update' services
now use encodedKey in APIs url:
Clients, Loans, Savings, Task
2.2  Removed wrappers for getting a List of Branches and Centres with
Full Details. For performance reasons using fullDetails parameter in
list APIs  is strongly discouraged by Mambu

3. Miscellaneous Changes:
3.1 added public method getMambuApiServiice() to all services to assist
with creation of common across services helper methods (for now used
this in Documents Service for getting documents APIs)
3.2 updated failing LoanTest to include new in 3.6 loan fields