Allow granting access to projects at global level.

Scenario:

1. Hundreds of projects, and hundreds of repositories in each project
2. A new group of users is created
3. You want to grant, e.g., read-only access to this group to all repositories

Problem:
It is very hard to achieve that, because a lot of manual work is required, even if project permissions are used.

Suggestion:
There should be an option to grant read-only access at the global level.

Workaround:
A script can be developed to make use of the available REST endpoints:

1. Call GET /rest/api/1.0/projects in order to retrieve a list of projects;
2. Iterate over the project names, calling PUT /rest/api/1.0/projects/{projectKey}/permissions/groups and grant PROJECT_READ permission to the group created.