Bug 23590: Add ability to edit the manager of a suggestion

Bug 23590: Add ability to edit the manager of a suggestion

Prior to this patch there was an hidden behavior that set the manager to
the logged in user when a suggestion was edited. This patch proposes to
let the librarian pick another manager.
Other small adjustements will be added to polish this new behavior:
 * Create 2 new DB columns: suggestions.lastmodificationby and
 suggestion.lastmodificationdate
 * Choose a manager when editing a suggestion
 * Batch modify suggestions and set a manager for them
 * Let notify the new manager using the TO_PROCESS letter
 * Display the manageddate, lastmodificationby and lastmodificationdate
 info where appropriate

This first patch adds a new "Select manager" link when editing a
suggestion.

Test plan for the whole patchset:
0/
  a. Execute the update DB entry, generate the new DBIC file and restart all
  b. Create at least 2 patrons with the suggestions_manage permission
1/ Submit a new suggestion (OPAC or staff, not important)
2/ Accept it
3/ Edit it
=> "Last modification by" is empty
=> You see that you are the manager of this suggestion
4/ Click "Select manager" and search for a new manager
=> The patron search will only display patrons with the
suggestions_manage permission
5/ Save
6/ Edit again
=> The manager is set to you, but there is a note saying that previously
it was the patron you picked
=> The "Last modification by" is set to you
7/ Click "Keep existing manager"
=> The manager is now set to the previous manager
8/ Select another manager (which has a valid email address defined)
9/ Click the "notify" checkbox
10/ Save
11/ Confirm that a TO_PROCESS notice has been generated into the
message_queue table
12/ Create at least one other suggestion
13/ List the suggestions
=> There is a 4th action column to assign a manager to several
suggestions in one go.
14/ Use this new button and confirm that it works as expected
15/ Go to your purchase suggestion list (OPAC and staff)
=> You see the "managed date" displayed in a new column

Sponsored-by: BULAC - http://www.bulac.fr/
Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>