Use a generic period rather than being hard coded
Whitespace
WIP: use new logic for completion graph
Standardise valueAttr across all collections

Grouped timeseries was using valueAttr and completion valueAttribute.
Switch everything to using valueAttr.
Tidy completion rate params

We know all of these values will exist as we set them in the
initializer, no need to pull them from the options.
Let comepletion rate collection be self supporting

The completion rate graph is now its own thing and doesn't extend the
completion collection. It also now lets backdrop do all the logic to
work out time buckets.

Updated the stagecraft stubs to include the actuall value attributes
which will come back from backdrop rather than trying to guess them.
Fix completion number graphs

They required the old behaviour. Fix them till they are refactored.
Refactor completion numbers and rate to share code

Move the work done on the completion rate graph into completion and make
it generic enough that it can also be used for the completion numbers
module. This means neither module will now have any hard coding on the
period or length of data which they can display. It also means they push
all the bucket size work off to backdrop rather than doing it
themselves.
Remove instance varables and handle null data

The tab instance variables are never used, we always use the optiions
object.

Handle the cases where there are no completions on a graph and where
there is no data coming back from backdrop.

Also remove extra comma on the end of collectionAttrs object.
Update backdrop stubs to match new requests
Update tests for new completion collections

As the number and rate collections don't contain any real logic any more
remove all the tests execpt those which check the methods they house.

Rewrite the completion collection tests now that there is no date logic
as most of the old tests are redundant.
Remove unused date functions

None of these are used any more after the completion rate graph has been
refactored.
Values are wrapped in backbone model, use getter

When wrapped in a backbone model you need to use a getter rather than
accessing the property directly.
Merge pull request #172 from alphagov/completion

Completion collections refactoring