Bug 16701: Translatability: Fix problem with isolated ' in currency.tt

Bug 16701: Translatability: Fix problem with isolated ' in currency.tt

This patch moves markup <span class="ex"> into template variables to
avoid sentence splitting.

To test:
- Apply patch
- Verify that currency administration works as before
  (Home > Administration > Currencies & Exchange rates > Currencies)
- Examine code changes

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit a83d75b6f2d59c3c2ac8d1b549b364fa79f52efe)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
(cherry picked from commit 538535ba7deb871d252b1afaf2ee4cb515350b98)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>