Bug 20226: Centralize update child code (CATCODE_MULTI)

Bug 20226: Centralize update child code (CATCODE_MULTI)

Code and variables to deal with the update child feature are not
centralized but copied/pasted in several scripts. Which leads to issues
obsviously (bug 20805 for instance).

Moreover the strings used by the templates are also in several template
files (or .inc)

To deal with that this patch introduces the idea to create 1 .inc file
per .js file
Here we have members-menu.inc for members-menu.js

Test plan:
- Remove all your adult categories (categories.category_type='A')
- Create a patron with a child category
- Try to update to adult category
=> The entry does no longer appears! (This is a change in the behaviour)
- Create one adult category
- Update to adult category
=> There is a JS confirmation message, if you accept the patron will
be updated to the adult category
- Create (at least) another adult category
- Create another child
- Update to adult category
=> No more confirmation message but a popup to select the adult category
- Pick one
=> The patron has been updated to the adult category

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>