Fix string display bug

For some text field questions, values containing quotes were being cut off when re-displayed in pages. There were two issues here: for textboxes the use of single quotes in the template meant that values with single quotes broke the template.  This is fixed by using double quotes in the templates.  For the dynamic textbox-input-list-item s there was a further problem with values being 'triple mustached' - i.e. not HTML-escaped.  Changing the script to use 'double mustacheing' instead fixes this.
Return user to summary page after clicking 'edit'

When you edit a page, saving your changes should return you to
the summary page.

The default flow is still to complete one page after another.

This commit add a URL parameter (`return_to_summary`). On the
'edit' links on the summary page it is set to `yes`.

When you view a page which has `?return_to_summary=yes` after the
URL the button will say 'Save and return to summary' rather than
'Save and continue'. Clicking the button will do what the button
says it does.
Remove legacy Boolean from method params
Removed debug gubbins
Merge pull request #129 from alphagov/save-and-return-to-summary

Return user to summary page after clicking 'edit' and saving
Added new AuthenticatingQuestionPage class which extends Authenticating controller and should be used for Question Pages
Listing class now contains a method to retreive a completed page by page_id
Removed debugging gubbins
QuestionPageDisplay now retrieves Page using the new getByPageId method in Listing, uses to load previously entered questions
Merge pull request #128 from alphagov/fix_string_display_again

Re-fix string display bug
Refactored all QuestionPages to extend new AuthenticatingQuestionPage class and use inherited methods for saving questions to pages
Remove old imports from Service.java
Removed logging stuff and email now loads from getEmail() method
Merge pull request #126 from alphagov/page_values_not_retaining_after_upload

Page values not retaining after upload
Display all error messages on all pages

Custom error messages were not being shown on all pages.

This introduces a new method on the Fixtures class that retrieves an
error message. It first checks if the message is a key in the
content.properties file. If not, it returns the message as is. This
allows custom messages to be defined in the controller where necesarry.
This was already being done but they weren't being displayed in the
frontend.

On questions with multiple text values (eg. features and benefits), only
one error is shown per question rather than one per question value.
Because of this the validation message has to be keyed by the question
key rather than the value key.
Update content to include latest changes
Add validation masthead on first two questions
Increase assurance max size to 60 characters

The largest assurance answer is now 55 characters long. This gives us a
small amount of buffer.
Display error messages on pages 14 and 24
Do not accept percent below 0 on q24