Introduce methods for reading tms-independed data in test context

[thiloSchlemmer]

Hi Loic,

again an other bit with is something like a prerequisite for pushing tilestitcher...

I found it useful, to have test-data, which can be used to create any tile, small, but with enough structure to test my testcases with neighbouring tiles (2 edges with the same vertices, 2 edges with different vertices).

As a result of this, i extracted the factory methods out to data-utils.py

[coveralls]

Coverage remained the same at 91.832% when pulling f3784879f8ebd80eb9b3d76e59b60eec4b7c3131 on thiloSchlemmer:Introduce_data-utils_and_tms-independed_Tests into 241a2a69f0c4ee9afdf2c77ff31856a89182788e on loicgasser:master.

[loicgasser]

This is dead code we can add it when needed.