Bug 18655: Correct the choose link in unimarc_field_210c value builder

Bug 18655: Correct the choose link in unimarc_field_210c value builder

- Link 'choose' is now a button.
- It doesn't call directly javascript anymore (use of listener).
- field to load stored in html on the page (less escaping needed).

Test plan :
1) Use UNIMARC catalog
2) Define unimarc_field_210c value builder on 210$c
3) Define an autority type EDITORS with heading on 200$b
4) Create an autority of this type with a single quote in heading, ie : l'avenir
5) Index this new autority
6) Edit a biblio record and launch 210$c value builder
7) Search for new autority
8) Click on 'Choose'
=> Heading should be pasted in 210$c

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>