[test]: unit tests for Statistics

[kwhuber]

From the testing checklist:

• Undergo initial load (delete current collection's CollectionPreferences and load stats, or use a database that hasn't been used with statistics before)
• Add new Shared page
• Add multiple pages
• Delete pages - verify there's no weird behavior
• Rename page with pencil icon
• Can't save a page without a name
• Verify adding long names looks okay
• Add new Private page
• Add multiple pages
• Delete pages - verify there's no weird behavior
• Edit an existing category
• Create new category
• Add several statistics
• Create new statistic
• Add stat item with same name, should have (2) after (-> see note)
• Rename stat item
• Save
• Delete new stat item
• Delete existing stat item
• Download as TSV
  • Should skip empty categories
• Try exporting when items are shown with NO PERMISSION, it should skip those items
• Make sure the section and page name is reflected in the file's name
• Button color preferences are respected in stats (-> see note)

Edit Permissions

• Verify you can grant edit access and assign it to a user
• Test the policies and roles you apply to a user
• Make sure edit button is not visible on shared statistics page
• Make sure 'save' and 'clone' are disabled from query
• No pencil or ‘+’ icon on shared layout pages
• Able to modify the query on a statistic
• Able to 'save' and 'clone'
• Can see pencil and ‘+’ icon on layout pages
• If you try going to a shared page while in the edit mode, the page should be disabled and statistics shouldn’t be clickable