Fix groupId of >75 age group

Attribute is returned from backdrop as an encoded entity, so it needs to be encoded in the config as well.
Add stub data for "time taken to complete transaction"

Correctly-formatted data is not yet in production (it's currently in
seconds rather than milliseconds) so it may be easiest to test
against this data.
Extend single-timeseries module with global format options

Create a module-wide set of format config options, so that
all elements of the module can refer to these options.

Pass these through the module and the view.
Extend duration formatters to return minutes and seconds

If passed 1234500ms and the 'm' unit option, return '20m 35s'.

The existing minute formatter isn't used anywhere in the app,
so just replace it.

This display option is for the time-taken-to-complete graph,
where data is most useful displayed in minutes and seconds.
Use a time scale in graph.js for duration data

Extend graph.js to use a time scale for data in duration format.
Set the domain of the scale using D3's .nice() function, not
by supplying an explicit domain and tick value list.

Supply the appropriate time interval to .nice() by looking
at the maximum value of the data.
Format submissions-graph y-axis for duration data

Use D3 time formats to display y-axis ticks nicely on our duration
graphs. Update tests.
Add time-taken-to-complete graph on Carer's Allowance
Set default formatting options at module level

Allow axes to over-ride individually if required.

Also update unit formatter for "time taken to complete" data
from "s" to "m", now that we are converting data into milliseconds
on the back-end.
Add line terminators to ends of line graphs

https://www.pivotaltracker.com/s/projects/911874/stories/74931512

It's not 100% obvious *exactly* what the requirements in the ticket are, but I think I've got them about right.

Also adds a bunch of tests for line terminator behaviour.
Correctly get configured period for timeshifted graphs

Timeshift line labels and tables were expecting period to be passed as an option

Get from `Collection#getPeriod` instead
Merge pull request #654 from alphagov/bugfix/timeshift-periods

Correctly get configured period for timeshifted graphs
Merge pull request #651 from alphagov/bugfix/voter-registration-age-groups

Fix groupId of >75 age group
Merge pull request #650 from alphagov/bugfix/line-terminators

Add line terminators to ends of line graphs
Fix site-activity config file against schema validation

Schema expects collect property to be an array.
Merge pull request #653 from alphagov/feature/time-taken-to-complete-graph

Feature/time taken to complete graph
Merge pull request #656 from alphagov/bugfix/site-activity-schema

Fix site-activity config file against schema validation