CustomResponse: fix log message.
Add translators.
remove broken docs link
Add logging of search quality information

For now, this only includes course id, search terms, and result count.
Information is logged both to the standard logger for near-term analysis
and the event tracker for the longer term. Result count logging requires
commit 02466b1 of cs_comments_service (otherwise it will be null).
Handle the indexerror exception on create_order
LMS-2646
Merge pull request #3641 from mlkwaqas/waqas/lms2646-list-index-error

Handle the indexerror exception on create_order
Revert "Handle the indexerror exception on create_order"
It was merged by mistake during the code freeze.
Merge pull request #3785 from mlkwaqas/waqas/lms2646-revert

Revert "Handle the indexerror exception on create_order"
Added sections on documenting and debugging, clarifications
Merge pull request #3777 from edx/ahodges/documentation/AN1031

Clarifications, added info on doc, format
Merge pull request #3644 from edx/db/remove-broken-docs-link

remove broken docs link
Merge pull request #3728 from edx/gprice/forum-search-logging

Add logging of search quality information
Merge pull request #3734 from edx/anton/i18n-custom-response

CustomResponse: fix log message.
Merge pull request #3715 from edx/anton/i18n-string-response

StringResponse i18n.
Tolerance expressed in percentage now computes correctly. [BLD-522]
Modified and extended tests on percentage expressed tolerance.
Addressed comments.
All tests pass now.
Added tests for compare_with_tolerance
Put unit tests of util in their own file.