Better validation of prices and percentages

Latest price validation didn't allow decimals - this allows either zero or two decimal places.
Percentage allowed e.g. '33.33d' as a value - this adds a regex to enforce digits and one decimal place only.
Allow user to specify versions of IE they support

Updates the content to include [pull request #26](https://github.com/alphagov/digital-marketplace-ssp-content/pull/26)
from the content
JSON encode and export all completed listings on a schedule

We want to export all completed listings to S3 on a schedule.
This commit adds JSON encoding to the listings and a new controller that is activated on a cron schedule to export a JSON file to S3 for each completed listing, to a new folder for each day.
Move class to test package as only used for testing
Use a task queue for JSON exports

In case the export job takes too long, we can add each export to a task queue to run in the background as a series of individual calls to S3.
Merge pull request #164 from alphagov/export_completed_listings_to_s3

Export completed listings to s3
Merge pull request #171 from alphagov/make_number_validation_better

Better validation of prices and percentages
Merge pull request #172 from alphagov/levels-of-IE-support

Allow user to specify versions of IE they support
Fix word count in controllers

The number of words in text boxes with a word count were being incorrectly calculated for cases when the submitted value contained multiple spaces in a row.