Add a "test" flag to plans about roadmap

[briri]

Decided to store 'is_test' and 'is_public' as separate boolean values to the projects table rather than as a value from a separate 'visibility_types' table like we have in the DMPTool codebase.

A plan can have the following visibilities:

• Test - visible only to the owner and specified collaborators
• Public - the plan will be available on the new Public DMPs page and accessible/exportable by anyone
• Organisational - the plan is neither Test or Public and is available to the owner, collaborators and admins

I'm handling the logic to prevent a plan from being marked as both public and test at the same time in the model and UI code.

Took an initial stab at the UX workflow for this and the new 'test' flag (see screenshots).

[briri]

Decided to switch to a visibilities table after discussion with @stephaniesimms. There are some nuances between making a plan 'test' and 'private' so we will need 4 visibility settings: test, private, organisational (default) and public

[briri]

related to #84

[stephaniesimms]

adding reference to Pivotal ticket for test flags: https://www.pivotaltracker.com/story/show/120867001

Objective is to mark test plans to separate them from usage stats. Possible ways to do this:

• add button/check box in Create plan workflow to mark test plans
• add button on Confirm plan details page (currently Create plan, Cancel options)
• test plan can be copied as a real plan or reclassified on My Plans page
• test plan cannot be exported

[briri]

Added test checkbox to view plans table. Only owners and coowners can change whether or not a plan is designated as a test. Making a plan 'test' will automatically change the visibility to 'Private' in the UI (the test flag is treated the same as the other visibilities in the database)

Also added the new 'create test plan' link which will bring the user to the create plan page.
I also added a configurable default visibility setting to the application.rb file. A new plan is automatically set to 'private' visibility. This can be overriden though for each installation.
When the user clicks 'create test plan' they will see the following:

[stephaniesimms]

test flag functionality works as expected. I can either create a Test plan at the outset, or tick the "Test" box in My plans or Plan details pages, which defaults the plan to private visibility. moving this issue along.

[sjDCC]

Looks good. Can create a test plan from scratch and easily adjust setting in table. This seems to autosave as just need to check box and entry is retained, which fits well with how we're implementing it elsewhere. Good to close out.