Vectors refactoring in Group package (Group class)

[KrystianKedron]

• Convert vector to List in Group class
• Add integration test for package Group classes

Fixes:

• Fix possible NPE in the Group.add_i method
• Fix recursion in the Group.get_device_i

Improvements:

• Simplify the conditions.
• Extend the JTangoTest and NoDBDeviceManager class to add possibility to run multiple devices for tests.

[KrystianKedron]

94

This PR depends on the changes in https://github.com/tango-controls/JTango/pull/110 and https://github.com/tango-controls/JTango/pull/111

Should be merged after this PR.