Added mock python modules for API python documentation

[akmorrow13]

No description provided.

[akmorrow13]

@heuermh fixes warnings in current docs:

WARNING: autodoc: failed to import module u'bdgenomics.adam.adamContext'; the following exception was raised:
No module named py4j.java_gateway
WARNING: autodoc: failed to import module u'bdgenomics.adam.rdd'; the following exception was raised:
No module named py4j.java_gateway
looking for now-outdated files... none found

[coveralls]

Coverage remained the same at 79.186% when pulling cbcd182 on akmorrow13:update-docs into 1ad572b on bigdatagenomics:master.

[AmplabJenkins]

Test PASSed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/ADAM-prb/2855/
Test PASSed.

[heuermh]

Thank you, @akmorrow13!