Issue 585: Ensure that users cannot be added to "New" / "Inactive" / "Archived" projects

[adeng27]

Description

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The views where users could be added to projects were updated to be blocked for all projects that do not have the Active status.

Checks for the Project Detail Page:
PIs/Managers for a certain project can add other users to the project via the Add Users button under Manage Project. This button is disabled if the given project's status is not Active. If the user attempts to bypass this check by adding add-users-search/ to their URL (thus accessing the ProjectAddUsersSearchView, they are redirected back to the Project Detail page and an error message appears.

• The ProjectAddUsersSearchResultsView is also blocked off for all projects without an Active status.

Checks for Join Page:
Users may send a join request for a project by navigating to /project/join/, where all projects with Active statuses are placed in a list. The ProjectJoinView was also blocked off for all non-active projects.

Fixes #585

Type of change

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• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

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• Manually checked that there was no way to add users to Inactive, Archived, or New projects.
• Wrote/updated unit tests in coldfront.core.project.tests.test_views.test_add_user_views and coldfront.core.project.tests.test_views.test_join_views.

PR Self Evaluation

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• My code follows the agreed upon best practices
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if needed)
• My changes generate no new warnings
• Any dependent changes have been merged and published in the appropriate modules
• I have performed a self-review of my own code