Add support to 1:1 relations (vector joins)

[volterra79]

Depends on:

• https://github.com/g3w-suite/g3w-admin/pull/599
• https://github.com/g3w-suite/g3w-client/pull/483

Demo project --> projects.zip

• father_join

• child_join

G3W-ADMIN Configuration --> Configure and activate layer editing

QGIS configuration --> 16.1.10. Joins Properties

[Raruto]

@leolami @volterra79 it's an intended behavior that the change_toolbox_relation message (within the left sidebar) disappears after activating editing on new a layer?

https://github.com/g3w-suite/g3w-client-plugin-editing/blob/ed935a9b8f23f4e6b790870c436860d01c61db4d/config/i18n/en.js#L97

[volterra79]

@Raruto i think could be better to leave it visible.