Bug 29588: (bug 29478 follow-up) Make strings translatable

Bug 29588: (bug 29478 follow-up) Make strings translatable

"or", "Yesterday", "Today" and "Tomorrow" are not translatable, we are
using __ when _ should be used (__ is for .js files only).

Test plan:
0. Apply the patch
1. cd misc/translator && perl translate update fr-FR
2. Edit misc/translator/po/fr-FR-staff-prog.po
Search for "or", "Yesterday", "Today" and "Tomorrow" and translate them
3. cd misc/translator && perl translate install fr-FR
4. Enable fr-FR (syspref 'language')
5. Edit a patron and an item and confirm that the flatpickr widget has
the strings correctly translated

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: ThibaudGLT <thibaud.guillot@biblibre.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>