Bug 9016: Create a message for each transport type.

Bug 9016: Create a message for each transport type.

This patch adds:
- a new jquery plugin : insertatcaret.
- the ability to define a notice template for each transport type.
- a new routine C4::Letters::GetMessageTransportTypes.

Test plan:
- Go on tools/letter.pl and check that all existing notices are still
  there.
- Modify one. A new empty message is present for sms, print, etc. The
  email message is filled with the existant value.
- Add a message for sms for example (don't forget the subject) and save.
- edit again and verify the sms message has been saved.

Signed-off-by: Olli-Antti Kivilahti <olli-antti.kivilahti@jns.fi>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>