Add Tag model to be able to tag Event

[yanicolivier]

Q	R
Type of contribution ?	[Features]
Tickets (issues) concerned	[278]

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What have you changed ?

I have added a Tag model into volunteer app to be able to tag the events.

Verification :

• My branch name respect the standard defined in CONTRIBUTING.md
• All my commits respect the standard defined in CONTRIBUTING.md
• This Pull-Request fully meets the requirements defined in the issue
• I added or modified the attached tests
• I added or modified the documentation

[coveralls]

Coverage remained the same at 0.0% when pulling 6c49e64 on yanicolivier:feature-tags_events into 0ce8df0 on Volontaria:develop.

[RignonNoel]

@yanicolivier Great job!

Here are the last things i thing we miss to finish this nice feature!

Test that we can filter the event by tag (would be nice to be sure it work :p)
Test that the tag are correctly created when creating an Event with tag directly
Test that we can add existing tag during event creation (and that it does not create a duplicated tag)
Test that the tag are correctly created when updating an Event with tag directly
Test that we can add existing tag during event update (and that it does not create a duplicated tag)

[yanicolivier]

@RignonNoel I'm facing a problem with this : Test that we can add existing tag during event creation (and that it does not create a duplicated tag)

I have created and commented a test line 144 of test_view_events.py.

Using WritableNestedModelSerializer seem to create the problem that I cannot add in a m2m an array of link to existing tags.

I have tried several approches to POST a new event with existing TAG without result. It's always asking to enter the name of the tag.

A strategy would be appreciated !