docs: nit-picky documentation

* Adding nit-picky sphinx-build in travis build.
* Commenting out all the badly commented modules.
* Adding placeholder documents for missing pages.

**Build is failing**
```
FAIL: test_error_catching (invenio.modules.records.testsuite.test_record.TestMarcRecordCreation)

----------------------------------------------------------------------

Traceback (most recent call last):

File "/home/travis/build/greut/invenio/invenio/modules/records/testsuite/test_record.py", line 571, in test_error_catching

schema='xml'

AssertionError: ReaderException not raised
```