admin: Rename "Contact mail" to "Contact email"

Fix apyrgio/synnefo#137
admin: Replace "snf-" with BACKEND_PREFIX_ID
admin: Add RBAC

The definition of which groups can author actions is kept in the conf
file of admin and has the following structure:

ADMIN_RBAC = {
    'user': {
        'activate': ['admin', 'helpdesk'],
        .
        .
        .
    },
    'vm': {...},
    .
    .
    .
}

That is, the main entry point is ADMIN_RBAC, which is a dictionary. The
first level of this dictionary is the target category of an action, e.g.
user, vm, volume etc. The second level is the action, which points to a
list of groups that can author it.

Fix apyrgio/synnefo#149
admin: Rename "Base" projects to "System" projects

Fix apyrgio/synnefo#141
admin: Link to associated item in table summary

When an associated item is shown in the summary of an item, add a link
to its details page.

Fix apyrgio/synnefo#140
Merge branch 'feature-admin-0.16-issues' into feature-admin