Log request and response basic data

@robyoung
@maxfliri
Removing tests around logging

@robyoung
@maxfliri
PEP8

@robyoung
@maxfliri
Fix validation of multi valued parameters.

@maxfliri
@robyoung
Force MultiDict for validation testing

@maxfliri
@robyoung
Add generic message for http errors

@robyoung
@maxfliri
Record update time when storing a document

@robyoung
@maxfliri
Merge pull request #52 from alphagov/common-error-messages

Add generic message for http errors
Replace inheritance with composition in validator
Use python 2.6 set syntax
Merge pull request #51 from alphagov/validate-multiple-collect-params

Validate multi-valued params
Merge pull request #54 from alphagov/record-document-update-timestamp

Record update time when storing a document
Merge branch 'master' into log-request-and-response

Conflicts:
	backdrop/read/api.py
Both 'start_at' and 'end_at' are required

It shouldn't be possible to query for open-ended
periods. It can be used to identify individual
licence events.
Merge pull request #55 from alphagov/extend-period-queries-validation

Both 'start_at' and 'end_at' are required
Allow querying of true / false values

@pbadenski
@gtrogers
Test for grouping on boolean values

@pbadenski
@gtrogers
Merge pull request #56 from alphagov/true_false

Allow querying of true / false values
requirements_for_tests.txt now includes requirements.txt

@maxfliri
files generated by jenkins.sh added to .gitignore

@maxfliri