Bug 34214: Make 'icon' configurable for Toolbar options

Bug 34214: Make 'icon' configurable for Toolbar options

Bug 33417 added a generic 'Toolbar' Vue component but always add a 'plus' icon. We should make it configurable.

Test plan:
Regenerate the Vue app: `yarn js:build`
Go to the ERM module and confirm that the toolbar has the '+' icon.

Sponsored-by: BULAC - http://www.bulac.fr/
Signed-off-by: Alexander Blanchard <alexander.blanchard@ptfs-europe.com>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>