Added a generic (template) file to hold common templates, added a template function to render list of groups (collapsible), reworked the admin interface to send newsletters

Signed-off-by: emanuele <emanuele45@gmail.com>
Missing file...

Signed-off-by: emanuele <emanuele45@gmail.com>
Renamed Helpers.template.php to GenericHelpers.template.php - thanks eurich for the suggestion

Signed-off-by: emanuele <emanuele45@gmail.com>
Moved template_select_boards to GenericHelpers

Signed-off-by: emanuele <emanuele45@gmail.com>
A couple of comments removed

Signed-off-by: emanuele <emanuele45@gmail.com>
Merge pull request #818 from emanuele45/newsletter

Some themes-related things (including rework of newsletters interface